[Chromium] Add GL_CHROMIUM_pixel_transfer_buffer_object extension support.
https://bugs.webkit.org/show_bug.cgi?id=102528

Patch by David Reveman <reveman@chromium.org> on 2012-11-22
Reviewed by James Robinson.

Add mapBufferCHROMIUM and unmapBufferCHROMIUM prototypes to WebGraphicsContext3D.h.

* chromium/public/WebGraphicsContext3D.h:
(WebGraphicsContext3D):
(WebKit::WebGraphicsContext3D::mapBufferCHROMIUM):
(WebKit::WebGraphicsContext3D::unmapBufferCHROMIUM):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk/Source/Platform/chromium/public@135530 268f45cc-cd09-0410-ab3c-d52691b4dbfc