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VideoFrames marked with VideoFrameMetadata::READ_LOCK_FENCES_ENABLED
must be retained until all reads have been completed. Such frames are
produced when software frames are uploaded to GpuMemoryBuffers. The
VideoResourceUpdater handles this, but PaintCanvasVideoRenderer
implemented only sync tokens.

As a result, WebGL reads of software-decoded frames can tear when the
storage is reused for later frames.

This CL adds a GL_COMMANDS_COMPLETED_CHROMIUM query after each potential
VideoFrame read in PaintCanvasVideoRenderer, and retains a reference to
the VideoFrame until it completes. This ensures that the memory is not
reused until after the reads complete in the GPU process.

TBR=tedchoc@chromium.org,pfeldman@chromium.org

Bug: 819914
Cq-Include-Trybots: luci.chromium.try:mac_optional_gpu_tests_rel
Change-Id: Iec05d3bca69e68ae3d3b231db84caa9bed24d777
Reviewed-on: https://chromium-review.googlesource.com/c/1258212
Commit-Queue: Dan Sanders <sandersd@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596072}