Added a RenderBuffer/RenderBufferInterface getTextureStorage method. Change-Id: I710fba737524e735349ce1c0b09fa535555bd029 Reviewed-on: https://chromium-review.googlesource.com/177034 Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Commit-Queue: Shannon Woods <shannonwoods@chromium.org> Tested-by: Shannon Woods <shannonwoods@chromium.org>