compute pressure: Ignore std::nullopt samples in CpuProbeManager

CpuProbes can produce std::nullopt samples when a value when an invalid
value is retrieved from the platform or, in the case of a fake probe (be
it system_cpu::FakeCpuProbe or the virtual probes used by WebDriver),
when CpuProbeManager starts asking for samples before a fake value has
been set.

Before this CL, this meant that there was a short window in web tests
between PressureObserver.observe() and update_virtual_pressure_source()
being called where VirtualCpuProbe would call
CpuProbeManager::OnCpuSampleAvailable() with std::nullopt and it would
end up being converted to a "nominal" pressure state, resulting in an
extra, unexpected update being delivered to PressureObserver that could
cause some web tests to fail.

We now only deliver updates if we got a valid sample from the probe.

Bug: 347031400
Change-Id: I37ae216ee13fff81177f6ddb0fa77fe7910132be
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5907628
Commit-Queue: Raphael Kubo Da Costa <raphael.kubo.da.costa@intel.com>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1364385}
3 files changed
tree: 013a516be57eb350d2209e3c34cdcb51397e8974
  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. google_update/
  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. WATCHLISTS
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