debugger statement is ignored in iframes removed from the document

This patch is conditioning the message `ContextWillBeDestroyed` to `MainThreadDebugger` during context disposal to happen only if the reason we are disposing the context is not `ClearForClose`.
The reason for such change is that the context of a detached iframe can still be used to execute code via iframe's `eval` and it would be useful to debug such code.
`ContextWillBeDestroyed` sends V8Inspector a `contextDestroyed` message where the inspector disposes data structures related with that context. Such message is also sent to V8Inspector when a context gets collected
by V8 GC, meaning that we were prematurely disposing such data
structures during frame dettachment and disallowing debuggability for
code using those contexts.
Since InspectedContexts holds a weak reference to a context and there's no strong reference from V8Inspector, this change doesn't leak memory by
holding contexts alive. Since there are multiple tests that rely on
`Runtime.executionContextDestroyed` message, we updated them to perform a GC after frame detachment, so the test could still work as expected.

Bug: 1015462
Change-Id: I6014bd8ddbfb1d3838b5364ccc9520b3b363b5fd
Reviewed-by: Nate Chapin <>
Reviewed-by: Mathias Bynens <>
Reviewed-by: Andrey Kosyakov <>
Reviewed-by: Simon Zünd <>
Commit-Queue: José Dapena Paz <>
Cr-Commit-Position: refs/heads/master@{#908362}
26 files changed
tree: d8ed1c5976aee5cdf78b1c970c83f2e3d386add7
  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. cloud_print/
  13. codelabs/
  14. components/
  15. content/
  16. courgette/
  17. crypto/
  18. dbus/
  19. device/
  20. docs/
  21. extensions/
  22. fuchsia/
  23. gin/
  24. google_apis/
  25. google_update/
  26. gpu/
  27. headless/
  28. infra/
  29. ios/
  30. ipc/
  31. jingle/
  32. media/
  33. mojo/
  34. native_client_sdk/
  35. net/
  36. pdf/
  37. ppapi/
  38. printing/
  39. remoting/
  40. rlz/
  41. sandbox/
  42. services/
  43. skia/
  44. sql/
  45. storage/
  46. styleguide/
  47. testing/
  48. third_party/
  49. tools/
  50. ui/
  51. url/
  52. weblayer/
  53. .clang-format
  54. .clang-tidy
  55. .eslintrc.js
  56. .git-blame-ignore-revs
  57. .gitattributes
  58. .gitignore
  59. .gn
  60. .mailmap
  61. .vpython
  62. .vpython3
  63. .yapfignore
  67. codereview.settings
  68. DEPS
  72. LICENSE.chromium_os
  73. OWNERS

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