Add a use counter for deprecated //@ in source map comment

We want to gauge the usage of the //@ prefix for sourceMappingUrl
comments. We already landed a histogram in https://crrev.com/c/4905898
but we'll revert the histogram in favour of a simple use counter.

The reason is that V8 background parsing only supports use counters
and not histograms and a use counter is sufficient for initial
analysis.

R=mlippautz@chromium.org

Bug: chromium:1488367
Change-Id: I6ed9e72665412af10d5e4607555cb270da157e4d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4909955
Commit-Queue: Simon Zünd <szuend@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1205692}
3 files changed
tree: 2f34ede73f7e79bdbe9c83b5af4bed13f3ea905a
  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. courgette/
  16. crypto/
  17. dbus/
  18. device/
  19. docs/
  20. extensions/
  21. fuchsia_web/
  22. gin/
  23. google_apis/
  24. google_update/
  25. gpu/
  26. headless/
  27. infra/
  28. ios/
  29. ipc/
  30. media/
  31. mojo/
  32. native_client_sdk/
  33. net/
  34. pdf/
  35. ppapi/
  36. printing/
  37. remoting/
  38. rlz/
  39. sandbox/
  40. services/
  41. skia/
  42. sql/
  43. storage/
  44. styleguide/
  45. testing/
  46. third_party/
  47. tools/
  48. ui/
  49. url/
  50. webkit/
  51. .clang-format
  52. .clang-tidy
  53. .eslintrc.js
  54. .git-blame-ignore-revs
  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. DEPS
  69. DIR_METADATA
  70. LICENSE
  71. LICENSE.chromium_os
  72. OWNERS
  73. PRESUBMIT.py
  74. PRESUBMIT_test.py
  75. PRESUBMIT_test_mocks.py
  76. README.md
  77. WATCHLISTS
README.md

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