[MVT Customization] Update / add metrics.

This CL adds metrics for the Most Visited Tiles Customization features
on Clank.

Existing:
1. Custom tile impression (split by positions):
   * NewTabPage.SuggestionsImpression.custom_links
2. Custom tile click (split by positions):
   * NewTabPage.MostVisited.custom_links
3. Context menu item usage: Pin, unpin, edit:
   * User.Actions =>
     Suggestions.ContextMenu.{PinItem,UnpinItem,EditItem}.

Renames:
4. "Add new" button click:
   * Old: User.Actions => MostVisited_AddItem.
   * New: User.Actions => Suggestions.Button.AddItem.

Added:
5. On-unpin snackbar "Undo" click:
   * User.Actions => Suggestions.SnackBar.UndoUnpinItem.
6. Drag-and-drop reordering:
   * User.Actions => Suggestions.Drag.ReorderItem.
7. Number of Custom Tiles on load: Take the simple approach of logging
   on first call of CustomLinksStore::RetrieveLinks():
   * NewTabPage.FirstLoad.NumberOfCustomTiles.

Bug: 420975821
Change-Id: I420bda8cbcfd740608403f09df6cb5b1c7eb9a62
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6596996
Commit-Queue: Samuel Huang <huangs@chromium.org>
Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
Reviewed-by: Tibor Goldschwendt <tiborg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1467450}
8 files changed
tree: 5a0fd71271f21e25455a21adfa57fdaa04442822
  1. .github/
  2. android_webview/
  3. apps/
  4. ash/
  5. base/
  6. build/
  7. build_overrides/
  8. buildtools/
  9. cc/
  10. chrome/
  11. chromecast/
  12. chromeos/
  13. codelabs/
  14. components/
  15. content/
  16. crypto/
  17. dbus/
  18. device/
  19. docs/
  20. extensions/
  21. fuchsia_web/
  22. gin/
  23. google_apis/
  24. gpu/
  25. headless/
  26. infra/
  27. ios/
  28. ipc/
  29. media/
  30. mojo/
  31. native_client_sdk/
  32. net/
  33. pdf/
  34. ppapi/
  35. printing/
  36. remoting/
  37. rlz/
  38. sandbox/
  39. services/
  40. skia/
  41. sql/
  42. storage/
  43. styleguide/
  44. testing/
  45. third_party/
  46. tools/
  47. ui/
  48. url/
  49. webkit/
  50. .clang-format
  51. .clang-tidy
  52. .clangd
  53. .git-blame-ignore-revs
  54. .gitallowed
  55. .gitattributes
  56. .gitignore
  57. .gitmodules
  58. .gn
  59. .mailmap
  60. .rustfmt.toml
  61. .vpython3
  62. .yapfignore
  63. ATL_OWNERS
  64. AUTHORS
  65. BUILD.gn
  66. CODE_OF_CONDUCT.md
  67. codereview.settings
  68. CPPLINT.cfg
  69. CRYPTO_OWNERS
  70. DEPS
  71. DIR_METADATA
  72. LICENSE
  73. LICENSE.chromium_os
  74. OWNERS
  75. PRESUBMIT.py
  76. PRESUBMIT_test.py
  77. PRESUBMIT_test_mocks.py
  78. README.md
  79. SECURITY_OWNERS
  80. WATCHLISTS
README.md

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