Fix unreliable MediaStream capture from WebGL canvases

Fix unreliable MediaStream capture from WebGL canvases

When capturing a MediaStrem from a WebGL canvas that
has the preserveDrawingBuffer option set to false, it is important
to perform the frame capture before the canvas is cleared by the
buffer swap mechanism.  This change resolves the issue by performing
the capture during the paint invalidation phase instead of during
frame finalization.  For canvases that are not visible on screen,
there is no paint invalidation, which is a problem. So in that
case, we fall back to doing the capture during frame finalization,
which is okay in that case because there is no buffer swap.

BUG=702446
Review-Url: https://codereview.chromium.org/2768683002
Cr-Commit-Position: refs/heads/master@{#460159}
(cherry picked from commit 7b09536cad07c7983eac63eac07ecf82f53c65d1)

Review-Url: https://codereview.chromium.org/2797543002 .
Cr-Commit-Position: refs/branch-heads/3029@{#553}
Cr-Branched-From: 939b32ee5ba05c396eef3fd992822fcca9a2e262-refs/heads/master@{#454471}
Committed: https://chromium.googlesource.com/chromium/src/+/d5af69c1ae0e600b758d1ae5dba6ead266826d13

[Justin Novosad, 2017-04-03 19:55:12]

Description was changed from

==========
Fix unreliable MediaStream capture from WebGL canvases

When capturing a MediaStrem from a WebGL canvas that
has the preserveDrawingBuffer option set to false, it is important
to perform the frame capture before the canvas is cleared by the
buffer swap mechanism.  This change resolves the issue by performing
the capture during the paint invalidation phase instead of during
frame finalization.  For canvases that are not visible on screen,
there is no paint invalidation, which is a problem. So in that
case, we fall back to doing the capture during frame finalization,
which is okay in that case because there is no buffer swap.

BUG=702446

Review-Url: https://codereview.chromium.org/2768683002
Cr-Commit-Position: refs/heads/master@{#460159}
(cherry picked from commit 7b09536cad07c7983eac63eac07ecf82f53c65d1)
==========

to

==========
Fix unreliable MediaStream capture from WebGL canvases

When capturing a MediaStrem from a WebGL canvas that
has the preserveDrawingBuffer option set to false, it is important
to perform the frame capture before the canvas is cleared by the
buffer swap mechanism.  This change resolves the issue by performing
the capture during the paint invalidation phase instead of during
frame finalization.  For canvases that are not visible on screen,
there is no paint invalidation, which is a problem. So in that
case, we fall back to doing the capture during frame finalization,
which is okay in that case because there is no buffer swap.

BUG=702446

Review-Url: https://codereview.chromium.org/2768683002
Cr-Commit-Position: refs/heads/master@{#460159}
(cherry picked from commit 7b09536cad07c7983eac63eac07ecf82f53c65d1)

Review-Url: https://codereview.chromium.org/2797543002 .
Cr-Commit-Position: refs/branch-heads/3029@{#553}
Cr-Branched-From:
939b32ee5ba05c396eef3fd992822fcca9a2e262-refs/heads/master@{#454471}
Committed:
https://chromium.googlesource.com/chromium/src/+/d5af69c1ae0e600b758d1ae5dba6...
==========

[Justin Novosad, 2017-04-03 19:55:13]

Committed patchset #1 (id:1) manually as
d5af69c1ae0e600b758d1ae5dba6ead266826d13.