chrome/common/privacy_budget/privacy_budget_features.h - chromium/src - Git at Google

 // Copyright 2020 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #ifndef CHROME_COMMON_PRIVACY_BUDGET_PRIVACY_BUDGET_FEATURES_H_
 #define CHROME_COMMON_PRIVACY_BUDGET_PRIVACY_BUDGET_FEATURES_H_

 #include <string>

 #include "base/feature_list.h"
 #include "base/metrics/field_trial_params.h"

 namespace features {

 // # Encoding of IdentifiableSurfaces:
 //
 // When used in fieldtrial parameters, nn IdentifiableSurface is encoded as the
 // decimal representation of its ToUkmMetricHash() result. An
 // IdentifiableSurface::Type is encoded as the decimal representation of the
 // enum value.

 // Root feature for all identifiability study logic.
 //
 // If the feature is disabled, then this browser instance will not be
 // participating in the identifiability study. I.e. no identifiability metrics
 // will be recorded or reported.
 //
 // Enabling the feature doesn't automatically make this client part of the study
 // either.
 extern const base::Feature kIdentifiabilityStudy;

 // Each time the key study parameters change, the study generation also
 // increments. Reporting the study generation alongside metrics allows the data
 // from different study generations to be grouped independently.
 //
 // Changes to the study generation resets all persisted state for the
 // identifiability study.
 //
 // Parameter name: "Gen"
 // Parameter type: int
 extern const base::FeatureParam<int> kIdentifiabilityStudyGeneration;

 // Surfaces that should be excluded from reports.
 //
 // Parameter name: "BlockedHashes"
 // Parameter type: Comma separated list of decimal integers, each of which
 //     represents an IdentifiableSurface.
 //
 // When specifying these values on the command-line, the commas should be
 // escaped using URL encoding. I.e. '1,2' -> '1%2C2'.
 //
 // E.g.:
 //  * "258, 257" : Matches IdentifiableSurface::FromTypeAndToken(kWebFeature, 1)
 //                 and IdentifiableSurface::FromTypeAndToken(kWebFeature, 2)
 //
 // From 03/2021 the code no longer supports revoking a surface that was once
 // blocked either via "BlockedHashes" or "BlockedTypes".
 extern const base::FeatureParam<std::string>
     kIdentifiabilityStudyBlockedMetrics;

 // Surface types that should be excluded from reports.
 //
 // Parameter name: "BlockedTypes"
 // Parameter type: Comma separated list of decimal integers, each of which
 //                 represents an IdentifiableSurface::Type.
 //
 // When specifying these values on the command-line, the commas should be
 // escaped using URL encoding. I.e. '1,2' -> '1%2C2'.
 //
 // E.g.:
 //  * "1, 2" : Matches all surfaces with types kWebFeature and kCanvasReadback.
 //
 // From 03/2021 the code no longer supports revoking a surface that was once
 // blocked either via "BlockedHashes" or "BlockedTypes".
 extern const base::FeatureParam<std::string> kIdentifiabilityStudyBlockedTypes;

 // Number of expected identifiable surfaces that will be sampled.
 //
 // Each site you visit implicitly or explicitly observes various identifiable
 // bits of information. This is the number of potentially identifiable surfaces
 // that we expect will be sampled per client.
 //
 // * For now, allow (kIdentifiabilityStudyExpectedSurfaceCount or
 // kIdentifiabilityStudyBlocks) and kIdentifiabilityStudyReidSurfaceBlocks to be
 // specified at the same time.
 //
 // Parameter name: "Rho"
 // Parameter type: int
 extern const base::FeatureParam<int> kIdentifiabilityStudyExpectedSurfaceCount;

 // Surface types allowed in the random assignment. If the parameter is empty or
 // invalid all types can be sampled. This does not have any effect on meta
 // surfaces (type 7), which are sampled in any case.
 //
 // Parameter name: "AllowedRandomTypes"
 // Parameter type: Comma separated list of decimal integers, each of which
 //     represents an IdentifiableSurface::Type.
 //
 // When specifying these values on the command-line, the commas should be
 // escaped using URL encoding. I.e. '1,2' -> '1%2C2'.
 //
 // E.g.:
 //  * "1, 2" : Matches all surfaces with types kWebFeature and kCanvasReadback.
 extern const base::FeatureParam<std::string>
     kIdentifiabilityStudyAllowedRandomTypes;

 // Largest meaningful surface count. Based on observed data. In very rare cases
 // the overall number of surfaces will exceed this limit, but based on prior
 // measurements these cases account for a tiny fraction of the entire
 // population.
 constexpr int kMaxIdentifiabilityStudyExpectedSurfaceCount = 1500;

 // The limit for the optimistic naive budget for the identifiability study.
 //
 // Each surface that's reported back via metrics reduces the available budget.
 // No report sent back should exceed this budget. The unit of measurement for
 // the budget is currently one _median_ identifiable surface. Some surfaces may
 // be more expensive and some may be less expensive.
 //
 // This value cannot exceed kMaxIdentifiabilityStudyActiveSurfaceBudget.
 //
 // Parameter name: "Max"
 // Parameter type: int
 extern const base::FeatureParam<int> kIdentifiabilityStudyActiveSurfaceBudget;

 // This is a hardcoded maximum for the identifiability study budget. The actual
 // budget cannot exceed this value even if it's sent via a server-side
 // configuration.
 //
 // I.e. the following is always true:
 //
 //     active_surface_budget_ <= kMaxIdentifiabilityStudyActiveSurfaceBudget
 //
 // This restriction prevents `active_surface_budget_` being increased past this
 // hardcoded limit from a server-side configuration.
 constexpr int kMaxIdentifiabilityStudyActiveSurfaceBudget = 40;

 // Relative cost of individual surfaces.
 //
 // Parameter name: "HashCost"
 // Parameter type: Comma separated list of <surface-hash-in-decimal;cost-factor>
 //                 pairs.
 //
 // By default all surfaces cost 1 _average_ surface. Exceptions are noted
 // individually and by type. This parameter contains the per-surface costs.
 //
 // Costs are always specified in units of _average_ surface. The value can be
 // a float expressed in decimal.
 //
 // When specifying these values on the command-line, the commas and semicolons
 // should be escaped using URL encoding. I.e. '1;2,3;4' -> '1%3B2%2C3%3B4'.
 //
 // E.g.:
 //   * "257;0.5" : Sets the relative cost of 0.5 for
 //                 IdentifiableSurface::FromTypeAndToken(kWebFeature, 1).
 extern const base::FeatureParam<std::string> kIdentifiabilityStudyPerHashCost;

 // Selection rate for clusters of related surfaces.
 // Surface equivalence classes.
 //
 // Parameter name: "Classes"
 // Parameter type: Comma separated list of classes. Each class is a semicolon
 //                 separated list of surfaces. See examples below.
 //
 // The first surface in the list is the representative surface that forms the
 // basis for determining the cost for the entire class. I.e. the cost of the
 // first surface in the list is assumed to be the cost of _any subset_ of
 // surfaces in the set.
 //
 // Every surface in an equivalence class is assumed to be pairwise perfectly
 // correlated with all other surfaces in the set. For more details see
 // definition of SurfaceSetValuation::EquivalenceClassIdentifierMap.
 //
 // It is an error for a surface to appear in more than one equivalence class.
 //
 // For more details see `SurfaceSetValuation`.
 //
 // E.g.:
 //   * "1;2;3,4;5;6" : Defines two classes: {1,2,3} and {4,5,6}. The surface
 //     with ID 1 defines the cost of the entire class {1,2,3}. Similarly the
 //     surface with ID 4 defines the cost of the entire class {4,5,6}.
 //
 extern const base::FeatureParam<std::string>
     kIdentifiabilityStudySurfaceEquivalenceClasses;

 // Selection rate for clusters of related surface types.
 //
 // Parameter name: "TypeCost"
 // Parameter type: Comma separated list of <surface-type-in-decimal;cost-factor>
 //                 pairs.
 //
 // By default all surfaces cost 1 _average_ surface. Exceptions are noted
 // individually and by type. This parameter contains the per-type costs.
 //
 // Costs are always specified in units of _average_ surface. The value can be
 // a float expressed in decimal.
 //
 // When specifying these values on the command-line, the commas and semicolons
 // should be escaped using URL encoding. I.e. '1;2,3;4' -> '1%3B2%2C3%3B4'.
 //
 // E.g.:
 //   * "1;0.5" : Sets the relative cost of 0.5 for all surfaces of type
 //               kWebFeature.
 extern const base::FeatureParam<std::string> kIdentifiabilityStudyPerTypeCost;

 // Surface Sampling Blocks.
 //
 // Parameter name: "Blocks"
 // Parameter type: Comma separated list of blocks. Each block is a semicolon
 //                 separated list of surfaces. See examples below.
 //
 // If this parameter specifies more than one block then at the start of an
 // experiment generation the browser picks one of the blocks at random (see
 // `BlockWeights` for details on the random distribution). All surfaces in the
 // selected block are considered to be in the active set.
 //
 // * It is valid for a single surface to be a member of multiple blocks. The
 //   study only uses one block.
 //
 // * The index of the selected block is persisted. If a new configuration has
 //   the same generation (Gen) but a different value for the `Blocks` parameter,
 //   the client will select the block at the same offset as the one it
 //   previously selected.
 //
 // * Specifying a surface that is blocked (either via `BlockedHashes` or
 //   `BlockedTypes`) is an error.
 //
 // * For now, allow (kIdentifiabilityStudyExpectedSurfaceCount or
 // kIdentifiabilityStudyBlocks) and kIdentifiabilityStudyReidSurfaceBlocks to be
 // specified at the same time.
 //
 // E.g.:
 //   * "1;2;3,4;5;6,7;8;9" : Defines three blocks: {1,2,3}, {4,5,6}, and
 //     {7,8,9}.
 extern const base::FeatureParam<std::string> kIdentifiabilityStudyBlocks;

 // Selection Weights for Blocks.
 //
 // Parameter name: "BlockWeights"
 // Parameter type: Comma separated list of relative weights expressed as
 //                 integers.
 //
 // If this parameter is specified then it must specify a weight for each block
 // that is defined using the `Blocks` parameter. Each integer defines the
 // relative weight assigned to the block of surfaces at the corresponding index.
 // Random selection of a block uses the multinomial distribution resulting from
 // normalizing the weights.
 //
 // * All weights must be non-zero positive integers.
 //
 // * There must be exactly as many weights as there are blocks. If not, the
 //   client assumes that the distribution should be uniform.
 //
 // * If this parameter is not specified, then the client assumes that the blocks
 //   are to be selected based on a uniform distribution.
 //
 // E.g.:
 //   * "5,7,3" assigns the probabilities ⅓, 7/15, ⅕ respectively to the three
 //     blocks defined in `Blocks`.
 extern const base::FeatureParam<std::string> kIdentifiabilityStudyBlockWeights;

 // Per surface relative cost.
 //
 // Parameter name: "HashCost"
 // Parameter type: Comma separated list of <surface;cost> pairs.
 //
 // By default all surfaces cost 1 *average* surface. Exceptions are noted
 // individually and by type. This parameter contains individual costs.
 //
 // Costs are always specified in units of _average_ surface. The value can be
 // a float expressed in decimal.
 //
 // When specifying these values on the command-line, the commas and semicolons
 // should be escaped using URL encoding. I.e. '1;2,3;4' -> '1%3B2%2C3%3B4'.
 //
 // See SurfaceSetValuation for details on the costing model.
 //
 // E.g.:
 //   * "261;0.5" : Sets the relative cost of 0.5 for surface with ID 261, which
 //   is a surface of type kWebFeature and token 1.
 extern const base::FeatureParam<std::string> kIdentifiabilityStudyPerHashCost;

 // Per type relative cost.
 //
 // Parameter name: "TypeCost"
 // Parameter type: Comma separated list of <surface-type;cost> pairs.
 //
 // By default all surfaces cost 1 _average_ surface. Exceptions are noted
 // individually and by type. This parameter contains the per-type costs.
 //
 // Costs are always specified in units of _average_ surface. The value can be
 // a float expressed in decimal.
 //
 // When specifying these values on the command-line, the commas and semicolons
 // should be escaped using URL encoding. I.e. '1;2,3;4' -> '1%3B2%2C3%3B4'.
 //
 // See SurfaceSetValuation for details on the costing model.
 //
 // E.g.:
 //   * "1;0.5" : Sets the relative cost of 0.5 for all surfaces of type
 //               kWebFeature.
 extern const base::FeatureParam<std::string> kIdentifiabilityStudyPerTypeCost;

 // This is a hardcoded maximum for the probability of any single surface to be
 // reported as part of the experiment.
 //
 // For example, given the following parameters:
 //     kIdentifiabilityStudyBlocks = "1;2,1;3,4;5"
 //     kIdentifiabilityStudyBlockWeights = "1,1,1"
 // the surface 1 has probability 2/3 to be chosen.
 //
 // If, in the finch client configuration, a surface appears with total
 // probability higher than this threshold, the study will be deactivated for
 // this client and this client will not report any surface.
 constexpr double kMaxProbabilityPerSurface = 0.5;

 // Reid Surface Blocks.
 //
 // Parameter name: "ReidSurfaceBlocks"
 // Parameter type: Comma separated list of blocks. Each block is a semicolon
 //                 separated list of surfaces. See examples below.
 //
 // Each block is a list of surfaces for which we want to estimate the Reid
 // score. For each block, we will collect and send to the server 1 bit of data.
 //
 // * For now, allow (kIdentifiabilityStudyExpectedSurfaceCount or
 // kIdentifiabilityStudyBlocks) and kIdentifiabilityStudyReidSurfaceBlocks to be
 // specified at the same time.
 //
 // E.g.:
 //   * "1;2;3,4;5;6,7;8;9" : Defines three blocks: {1,2,3}, {4,5,6}, and
 //     {7,8,9}.
 extern const base::FeatureParam<std::string>
     kIdentifiabilityStudyReidSurfaceBlocks;

 }  // namespace features

 #endif  // CHROME_COMMON_PRIVACY_BUDGET_PRIVACY_BUDGET_FEATURES_H_
	// Copyright 2020 The Chromium Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#ifndef CHROME_COMMON_PRIVACY_BUDGET_PRIVACY_BUDGET_FEATURES_H_
	#define CHROME_COMMON_PRIVACY_BUDGET_PRIVACY_BUDGET_FEATURES_H_

	#include <string>

	#include "base/feature_list.h"
	#include "base/metrics/field_trial_params.h"

	namespace features {

	// # Encoding of IdentifiableSurfaces:
	//
	// When used in fieldtrial parameters, nn IdentifiableSurface is encoded as the
	// decimal representation of its ToUkmMetricHash() result. An
	// IdentifiableSurface::Type is encoded as the decimal representation of the
	// enum value.

	// Root feature for all identifiability study logic.
	//
	// If the feature is disabled, then this browser instance will not be
	// participating in the identifiability study. I.e. no identifiability metrics
	// will be recorded or reported.
	//
	// Enabling the feature doesn't automatically make this client part of the study
	// either.
	extern const base::Feature kIdentifiabilityStudy;

	// Each time the key study parameters change, the study generation also
	// increments. Reporting the study generation alongside metrics allows the data
	// from different study generations to be grouped independently.
	//
	// Changes to the study generation resets all persisted state for the
	// identifiability study.
	//
	// Parameter name: "Gen"
	// Parameter type: int
	extern const base::FeatureParam<int> kIdentifiabilityStudyGeneration;

	// Surfaces that should be excluded from reports.
	//
	// Parameter name: "BlockedHashes"
	// Parameter type: Comma separated list of decimal integers, each of which
	// represents an IdentifiableSurface.
	//
	// When specifying these values on the command-line, the commas should be
	// escaped using URL encoding. I.e. '1,2' -> '1%2C2'.
	//
	// E.g.:
	// * "258, 257" : Matches IdentifiableSurface::FromTypeAndToken(kWebFeature, 1)
	// and IdentifiableSurface::FromTypeAndToken(kWebFeature, 2)
	//
	// From 03/2021 the code no longer supports revoking a surface that was once
	// blocked either via "BlockedHashes" or "BlockedTypes".
	extern const base::FeatureParam<std::string>
	kIdentifiabilityStudyBlockedMetrics;

	// Surface types that should be excluded from reports.
	//
	// Parameter name: "BlockedTypes"
	// Parameter type: Comma separated list of decimal integers, each of which
	// represents an IdentifiableSurface::Type.
	//
	// When specifying these values on the command-line, the commas should be
	// escaped using URL encoding. I.e. '1,2' -> '1%2C2'.
	//
	// E.g.:
	// * "1, 2" : Matches all surfaces with types kWebFeature and kCanvasReadback.
	//
	// From 03/2021 the code no longer supports revoking a surface that was once
	// blocked either via "BlockedHashes" or "BlockedTypes".
	extern const base::FeatureParam<std::string> kIdentifiabilityStudyBlockedTypes;

	// Number of expected identifiable surfaces that will be sampled.
	//
	// Each site you visit implicitly or explicitly observes various identifiable
	// bits of information. This is the number of potentially identifiable surfaces
	// that we expect will be sampled per client.
	//
	// * For now, allow (kIdentifiabilityStudyExpectedSurfaceCount or
	// kIdentifiabilityStudyBlocks) and kIdentifiabilityStudyReidSurfaceBlocks to be
	// specified at the same time.
	//
	// Parameter name: "Rho"
	// Parameter type: int
	extern const base::FeatureParam<int> kIdentifiabilityStudyExpectedSurfaceCount;

	// Surface types allowed in the random assignment. If the parameter is empty or
	// invalid all types can be sampled. This does not have any effect on meta
	// surfaces (type 7), which are sampled in any case.
	//
	// Parameter name: "AllowedRandomTypes"
	// Parameter type: Comma separated list of decimal integers, each of which
	// represents an IdentifiableSurface::Type.
	//
	// When specifying these values on the command-line, the commas should be
	// escaped using URL encoding. I.e. '1,2' -> '1%2C2'.
	//
	// E.g.:
	// * "1, 2" : Matches all surfaces with types kWebFeature and kCanvasReadback.
	extern const base::FeatureParam<std::string>
	kIdentifiabilityStudyAllowedRandomTypes;

	// Largest meaningful surface count. Based on observed data. In very rare cases
	// the overall number of surfaces will exceed this limit, but based on prior
	// measurements these cases account for a tiny fraction of the entire
	// population.
	constexpr int kMaxIdentifiabilityStudyExpectedSurfaceCount = 1500;

	// The limit for the optimistic naive budget for the identifiability study.
	//
	// Each surface that's reported back via metrics reduces the available budget.
	// No report sent back should exceed this budget. The unit of measurement for
	// the budget is currently one _median_ identifiable surface. Some surfaces may
	// be more expensive and some may be less expensive.
	//
	// This value cannot exceed kMaxIdentifiabilityStudyActiveSurfaceBudget.
	//
	// Parameter name: "Max"
	// Parameter type: int
	extern const base::FeatureParam<int> kIdentifiabilityStudyActiveSurfaceBudget;

	// This is a hardcoded maximum for the identifiability study budget. The actual
	// budget cannot exceed this value even if it's sent via a server-side
	// configuration.
	//
	// I.e. the following is always true:
	//
	// active_surface_budget_ <= kMaxIdentifiabilityStudyActiveSurfaceBudget
	//
	// This restriction prevents `active_surface_budget_` being increased past this
	// hardcoded limit from a server-side configuration.
	constexpr int kMaxIdentifiabilityStudyActiveSurfaceBudget = 40;

	// Relative cost of individual surfaces.
	//
	// Parameter name: "HashCost"
	// Parameter type: Comma separated list of <surface-hash-in-decimal;cost-factor>
	// pairs.
	//
	// By default all surfaces cost 1 _average_ surface. Exceptions are noted
	// individually and by type. This parameter contains the per-surface costs.
	//
	// Costs are always specified in units of _average_ surface. The value can be
	// a float expressed in decimal.
	//
	// When specifying these values on the command-line, the commas and semicolons
	// should be escaped using URL encoding. I.e. '1;2,3;4' -> '1%3B2%2C3%3B4'.
	//
	// E.g.:
	// * "257;0.5" : Sets the relative cost of 0.5 for
	// IdentifiableSurface::FromTypeAndToken(kWebFeature, 1).
	extern const base::FeatureParam<std::string> kIdentifiabilityStudyPerHashCost;

	// Selection rate for clusters of related surfaces.
	// Surface equivalence classes.
	//
	// Parameter name: "Classes"
	// Parameter type: Comma separated list of classes. Each class is a semicolon
	// separated list of surfaces. See examples below.
	//
	// The first surface in the list is the representative surface that forms the
	// basis for determining the cost for the entire class. I.e. the cost of the
	// first surface in the list is assumed to be the cost of _any subset_ of
	// surfaces in the set.
	//
	// Every surface in an equivalence class is assumed to be pairwise perfectly
	// correlated with all other surfaces in the set. For more details see
	// definition of SurfaceSetValuation::EquivalenceClassIdentifierMap.
	//
	// It is an error for a surface to appear in more than one equivalence class.
	//
	// For more details see `SurfaceSetValuation`.
	//
	// E.g.:
	// * "1;2;3,4;5;6" : Defines two classes: {1,2,3} and {4,5,6}. The surface
	// with ID 1 defines the cost of the entire class {1,2,3}. Similarly the
	// surface with ID 4 defines the cost of the entire class {4,5,6}.
	//
	extern const base::FeatureParam<std::string>
	kIdentifiabilityStudySurfaceEquivalenceClasses;

	// Selection rate for clusters of related surface types.
	//
	// Parameter name: "TypeCost"
	// Parameter type: Comma separated list of <surface-type-in-decimal;cost-factor>
	// pairs.
	//
	// By default all surfaces cost 1 _average_ surface. Exceptions are noted
	// individually and by type. This parameter contains the per-type costs.
	//
	// Costs are always specified in units of _average_ surface. The value can be
	// a float expressed in decimal.
	//
	// When specifying these values on the command-line, the commas and semicolons
	// should be escaped using URL encoding. I.e. '1;2,3;4' -> '1%3B2%2C3%3B4'.
	//
	// E.g.:
	// * "1;0.5" : Sets the relative cost of 0.5 for all surfaces of type
	// kWebFeature.
	extern const base::FeatureParam<std::string> kIdentifiabilityStudyPerTypeCost;

	// Surface Sampling Blocks.
	//
	// Parameter name: "Blocks"
	// Parameter type: Comma separated list of blocks. Each block is a semicolon
	// separated list of surfaces. See examples below.
	//
	// If this parameter specifies more than one block then at the start of an
	// experiment generation the browser picks one of the blocks at random (see
	// `BlockWeights` for details on the random distribution). All surfaces in the
	// selected block are considered to be in the active set.
	//
	// * It is valid for a single surface to be a member of multiple blocks. The
	// study only uses one block.
	//
	// * The index of the selected block is persisted. If a new configuration has
	// the same generation (Gen) but a different value for the `Blocks` parameter,
	// the client will select the block at the same offset as the one it
	// previously selected.
	//
	// * Specifying a surface that is blocked (either via `BlockedHashes` or
	// `BlockedTypes`) is an error.
	//
	// * For now, allow (kIdentifiabilityStudyExpectedSurfaceCount or
	// kIdentifiabilityStudyBlocks) and kIdentifiabilityStudyReidSurfaceBlocks to be
	// specified at the same time.
	//
	// E.g.:
	// * "1;2;3,4;5;6,7;8;9" : Defines three blocks: {1,2,3}, {4,5,6}, and
	// {7,8,9}.
	extern const base::FeatureParam<std::string> kIdentifiabilityStudyBlocks;

	// Selection Weights for Blocks.
	//
	// Parameter name: "BlockWeights"
	// Parameter type: Comma separated list of relative weights expressed as
	// integers.
	//
	// If this parameter is specified then it must specify a weight for each block
	// that is defined using the `Blocks` parameter. Each integer defines the
	// relative weight assigned to the block of surfaces at the corresponding index.
	// Random selection of a block uses the multinomial distribution resulting from
	// normalizing the weights.
	//
	// * All weights must be non-zero positive integers.
	//
	// * There must be exactly as many weights as there are blocks. If not, the
	// client assumes that the distribution should be uniform.
	//
	// * If this parameter is not specified, then the client assumes that the blocks
	// are to be selected based on a uniform distribution.
	//
	// E.g.:
	// * "5,7,3" assigns the probabilities ⅓, 7/15, ⅕ respectively to the three
	// blocks defined in `Blocks`.
	extern const base::FeatureParam<std::string> kIdentifiabilityStudyBlockWeights;

	// Per surface relative cost.
	//
	// Parameter name: "HashCost"
	// Parameter type: Comma separated list of <surface;cost> pairs.
	//
	// By default all surfaces cost 1 average surface. Exceptions are noted
	// individually and by type. This parameter contains individual costs.
	//
	// Costs are always specified in units of _average_ surface. The value can be
	// a float expressed in decimal.
	//
	// When specifying these values on the command-line, the commas and semicolons
	// should be escaped using URL encoding. I.e. '1;2,3;4' -> '1%3B2%2C3%3B4'.
	//
	// See SurfaceSetValuation for details on the costing model.
	//
	// E.g.:
	// * "261;0.5" : Sets the relative cost of 0.5 for surface with ID 261, which
	// is a surface of type kWebFeature and token 1.
	extern const base::FeatureParam<std::string> kIdentifiabilityStudyPerHashCost;

	// Per type relative cost.
	//
	// Parameter name: "TypeCost"
	// Parameter type: Comma separated list of <surface-type;cost> pairs.
	//
	// By default all surfaces cost 1 _average_ surface. Exceptions are noted
	// individually and by type. This parameter contains the per-type costs.
	//
	// Costs are always specified in units of _average_ surface. The value can be
	// a float expressed in decimal.
	//
	// When specifying these values on the command-line, the commas and semicolons
	// should be escaped using URL encoding. I.e. '1;2,3;4' -> '1%3B2%2C3%3B4'.
	//
	// See SurfaceSetValuation for details on the costing model.
	//
	// E.g.:
	// * "1;0.5" : Sets the relative cost of 0.5 for all surfaces of type
	// kWebFeature.
	extern const base::FeatureParam<std::string> kIdentifiabilityStudyPerTypeCost;

	// This is a hardcoded maximum for the probability of any single surface to be
	// reported as part of the experiment.
	//
	// For example, given the following parameters:
	// kIdentifiabilityStudyBlocks = "1;2,1;3,4;5"
	// kIdentifiabilityStudyBlockWeights = "1,1,1"
	// the surface 1 has probability 2/3 to be chosen.
	//
	// If, in the finch client configuration, a surface appears with total
	// probability higher than this threshold, the study will be deactivated for
	// this client and this client will not report any surface.
	constexpr double kMaxProbabilityPerSurface = 0.5;

	// Reid Surface Blocks.
	//
	// Parameter name: "ReidSurfaceBlocks"
	// Parameter type: Comma separated list of blocks. Each block is a semicolon
	// separated list of surfaces. See examples below.
	//
	// Each block is a list of surfaces for which we want to estimate the Reid
	// score. For each block, we will collect and send to the server 1 bit of data.
	//
	// * For now, allow (kIdentifiabilityStudyExpectedSurfaceCount or
	// kIdentifiabilityStudyBlocks) and kIdentifiabilityStudyReidSurfaceBlocks to be
	// specified at the same time.
	//
	// E.g.:
	// * "1;2;3,4;5;6,7;8;9" : Defines three blocks: {1,2,3}, {4,5,6}, and
	// {7,8,9}.
	extern const base::FeatureParam<std::string>
	kIdentifiabilityStudyReidSurfaceBlocks;

	} // namespace features

	#endif // CHROME_COMMON_PRIVACY_BUDGET_PRIVACY_BUDGET_FEATURES_H_