Merge 135809 - [Chromium] Shared graphics context should only pushGroupMarker() once

Merge 135809 - [Chromium] Shared graphics context should only pushGroupMarker() once
https://bugs.webkit.org/show_bug.cgi?id=103082

Reviewed by James Robinson.

GraphicsContext3D's pushGroupMarkerEXT() is being called every time
an ImageBuffer is created, leading to unlimited memory growth, since
they share a common GraphicsContext3D.  It should be called only once,
on context creation.

See also http://crbug.com/160411.

Tested by manually checking the memory usage in Chrome's TaskManager.
(Sorry, I can't think of a way to test this automatically.)

* platform/graphics/gpu/SharedGraphicsContext3D.cpp:
(WebCore::SharedGraphicsContext3DImpl::getOrCreateContext):
* platform/graphics/skia/ImageBufferSkia.cpp:
(WebCore::createAcceleratedCanvas):


TBR=senorblanco@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=136023