Use the shared context for ppapi parenting

Use the shared context for ppapi parenting

This parents pepper 3d contexts to the shared graphics context and not directly to the compositor context.
This has two benefits:
1.) The shared context can be used from the main thread, unlike the compositor context in threaded mode
2.) The shared context is offscreen, so it can be initialized before the view's HWND/whatnot is ready

This depends on https://bugs.webkit.org/show_bug.cgi?id=80670

BUG=117125
TEST=load up ppapi/examples/gles2/gles.html with --enable-threaded-compositing. plugin should initialize and
render correctly in debug mode with no assertions about incorrect thread use, and the plugin should recover
and continue rendering if the GPU process is killed.


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=127057

[piman, 2012-03-09 06:35:32]

lgtm

[commit-bot: I haz the power, 2012-03-15 21:06:55]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jamesr@chromium.org/9657021/1

[commit-bot: I haz the power, 2012-03-16 00:59:39]

Change committed as 127057