+miu@ to help triage

Currently I'm seeing a few tests that utilize surface copying. They either have errors, or are timing out when attempting to determine if a surface can be copied.

GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestHiDPI.*
  - Currently fail with errors
GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestTabCapture.*
  - timeout
GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestTabCaptureHighDPI.*
  - timeout

Probably just that the tests depend on some signals not available when VIZ is enabled. These are very legacy tests, and they do a lot of "synchronization" (e.g., waiting for a first frame) that they really shouldn't have to do. They need to be spruced-up/rewritten, to be more like the WebContentsVideoCaptureDeviceBrowserTests.

Very likely missing signals for viz. Especially in cases where the tests are looping infinitely.

We've recently added support for synchronizing on frames and scroll positions in browser_tests_utils::RenderFrameSubmissionObserver.

However all the legacy surface waiting will likely need to be updated as you suggest.

These pass now:

rr ctbt --enable-features=VizDisplayCompositor --gtest_filter=*GLAndSoftwareCompositing*
....
[       OK ] GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestTabCaptureHighDPI.CopyToBitmap_ScaledResult/1 (1829 ms)
[----------] 1 test from GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestTabCaptureHighDPI (1829 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (1830 ms total)
[  PASSED  ] 1 test.
[16/18] GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestTabCaptureHighDPI.CopyToBitmap_ScaledResult/1 (2362 ms)
Note: Google Test filter = GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestHiDPI.ScrollOffset/0
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestHiDPI
[ RUN      ] GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestHiDPI.ScrollOffset/0

DevTools listening on ws://127.0.0.1:45203/devtools/browser/c78b9597-2094-4b7d-a9db-1f17bdad6e9a
[153396:153396:0516/135713.475790:INFO:CONSOLE(0)] "Using unescaped '#' characters in a data URI body is deprecated and will be removed in M68, around July 2018. Please use '%23' instead. See https://www.chromestatus.com/features/5656049583390720 for more details.", source:  (0)
[153421:153421:0516/135714.356847:ERROR:gles2_cmd_decoder.cc(18027)] [GroupMarkerNotSet( crbug.com/242999 )!:A8050348D1280000]GL ERROR :GL_INVALID_OPERATION : glCreateAndConsumeTextureCHROMIUM: invalid mailbox name
[153421:153421:0516/135714.356963:ERROR:gles2_cmd_decoder.cc(18027)] [GroupMarkerNotSet( crbug.com/242999 )!:A8050348D1280000]GL ERROR :GL_INVALID_OPERATION : glCreateAndConsumeTextureCHROMIUM: invalid mailbox name
[153421:153421:0516/135714.359393:ERROR:gles2_cmd_decoder.cc(10104)] [GroupMarkerNotSet( crbug.com/242999 )!:A8050348D1280000]RENDER WARNING: texture bound to texture unit 0 is not renderable. It maybe non-power-of-2 and have incompatible texture filtering.
[153421:153421:0516/135714.540838:ERROR:gles2_cmd_decoder.cc(10104)] [GroupMarkerNotSet( crbug.com/242999 )!:A8050348D1280000]RENDER WARNING: texture bound to texture unit 0 is not renderable. It maybe non-power-of-2 and have incompatible texture filtering.
[153396:153405:0516/135714.619736:WARNING:discardable_shared_memory_manager.cc(431)] Some MojoDiscardableSharedMemoryManagerImpls are still alive. They will be leaked.
[153396:153474:0516/135714.627932:WARNING:internal_linux.cc(64)] Failed to read /proc/153421/stat
[       OK ] GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestHiDPI.ScrollOffset/0 (2346 ms)
[----------] 1 test from GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestHiDPI (2346 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (2346 ms total)
[  PASSED  ] 1 test.
[17/18] GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestHiDPI.ScrollOffset/0 (2886 ms)
Note: Google Test filter = GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestHiDPI.ScrollOffset/1
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestHiDPI
[ RUN      ] GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestHiDPI.ScrollOffset/1
[153488:153488:0516/135716.347188:ERROR:viz_process_transport_factory.cc(378)] Switching to software compositing.

DevTools listening on ws://127.0.0.1:39413/devtools/browser/5bd6e0ea-910f-4560-b76c-24725e8d47f9
[153488:153488:0516/135716.457460:INFO:CONSOLE(0)] "Using unescaped '#' characters in a data URI body is deprecated and will be removed in M68, around July 2018. Please use '%23' instead. See https://www.chromestatus.com/features/5656049583390720 for more details.", source:  (0)
[153488:153495:0516/135717.085568:WARNING:discardable_shared_memory_manager.cc(431)] Some MojoDiscardableSharedMemoryManagerImpls are still alive. They will be leaked.
[153488:153539:0516/135717.093715:WARNING:internal_linux.cc(64)] Failed to read /proc/153510/stat
[       OK ] GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestHiDPI.ScrollOffset/1 (1896 ms)
[----------] 1 test from GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestHiDPI (1896 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (1896 ms total)
[  PASSED  ] 1 test.
[18/18] GLAndSoftwareCompositing/CompositingRenderWidgetHostViewBrowserTestHiDPI.ScrollOffset/1 (2619 ms)
SUCCESS: all tests passed.