gpu: Refactor GpuMemoryBuffer framework for multi-process support.

This removes the ImageFactory interface and adjusts the buffer
allocation system for future multi-process support.

Also includes proper plumbing of internalformat to GLImage implementation
and makes sure the compositor is using the correct format.

TEST=gpu_unittests --gtest_filter=MockGpuMemoryBufferTest.Lifecycle
BUG=261649

Review URL: https://chromiumcodereview.appspot.com/20017005
Signed-off-by: Chirayu Desai <cdesai@cyanogenmod.org>
Change-Id: Iff859f68f7097a36262bd24c0face0edf63f4a4c
Signed-off-by: Joel Teichroeb <joel@teichroeb.net>