[MaliciousApkDownloadCheck] Implement random sampling

This is part 5 of 6 of relanding code that was originally landed in
crrev.com/c/6309053 but was reverted.

This CL implements random sampling of eligible downloads, controlled by
a FeatureParam that is configurable via fieldtrial. This is separate
from the sampling of allowlisted downloads and the sampling of
unsupported filetypes, which are both supported on desktop platforms
but not Android.

Bug: 397407934
Change-Id: Ib0f07da7b6e4688c66a0b645e160cb0663a66dab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6341010
Commit-Queue: Lily Chen <chlily@chromium.org>
Reviewed-by: Daniel Rubery <drubery@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1434193}
8 files changed
tree: 826070b93d8d3e67d109f2330e7df2207bacd9aa
  1. android_webview/
  2. apps/
  3. ash/
  4. base/
  5. build/
  6. build_overrides/
  7. buildtools/
  8. cc/
  9. chrome/
  10. chromecast/
  11. chromeos/
  12. codelabs/
  13. components/
  14. content/
  15. crypto/
  16. dbus/
  17. device/
  18. docs/
  19. extensions/
  20. fuchsia_web/
  21. gin/
  22. google_apis/
  23. gpu/
  24. headless/
  25. infra/
  26. ios/
  27. ipc/
  28. media/
  29. mojo/
  30. native_client_sdk/
  31. net/
  32. pdf/
  33. ppapi/
  34. printing/
  35. remoting/
  36. rlz/
  37. sandbox/
  38. services/
  39. skia/
  40. sql/
  41. storage/
  42. styleguide/
  43. testing/
  44. third_party/
  45. tools/
  46. ui/
  47. url/
  48. webkit/
  49. .clang-format
  50. .clang-tidy
  51. .clangd
  52. .git-blame-ignore-revs
  53. .gitallowed
  54. .gitattributes
  55. .gitignore
  56. .gitmodules
  57. .gn
  58. .mailmap
  59. .rustfmt.toml
  60. .vpython3
  61. .yapfignore
  62. ATL_OWNERS
  63. AUTHORS
  64. BUILD.gn
  65. CODE_OF_CONDUCT.md
  66. codereview.settings
  67. CPPLINT.cfg
  68. CRYPTO_OWNERS
  69. DEPS
  70. DIR_METADATA
  71. LICENSE
  72. LICENSE.chromium_os
  73. OWNERS
  74. PRESUBMIT.py
  75. PRESUBMIT_test.py
  76. PRESUBMIT_test_mocks.py
  77. README.md
  78. WATCHLISTS
README.md

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