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This adds single process support for IOSurface and
SurfaceTexture backed GpuMemoryBuffers.

Also makes the SurfaceTexture code more consistent
with IOSurface code by using a singleton instead of
leaking a raw pointer.

BUG=497559
TEST=content_browsertests --gtest_filter=ChildThreadImplGpuMemoryBufferBrowserTests/*

Review URL: https://codereview.chromium.org/1120873002

Cr-Commit-Position: refs/heads/master@{#333625}