[chromium] Rename non-standard discard/ensureFramebufferCHROMIUM extensions so we can use real GL_EXT_discard_framebuffer
https://bugs.webkit.org/show_bug.cgi?id=104316

Patch by James Robinson <jamesr@chromium.org> on 2012-12-06
Reviewed by Kenneth Russell.

GL_EXT_discard_framebuffer is a GL extension that enables optimizations for GPUs that aggressively defer
operations. We've 'borrowed' the extension namespace to enable backbuffer management, but this makes it
impossible to use the actual extension.  This adds new entry points for backbuffer management. After callers
(which aren't in the WebKit repo) are updated, we can remove the overlapping entry points.

* chromium/public/WebGraphicsContext3D.h:
(WebGraphicsContext3D):
(WebKit::WebGraphicsContext3D::discardFramebufferCHROMIUM):
(WebKit::WebGraphicsContext3D::discardBackbufferCHROMIUM):
(WebKit::WebGraphicsContext3D::ensureBackbufferCHROMIUM):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk/Source/Platform/chromium/public@136917 268f45cc-cd09-0410-ab3c-d52691b4dbfc