cmaa, gpu: use R8 image texture when GL_NV_image_formats is available.
Recently Mesa supports GL_NV_image_formats extension for r8 image texture for ES 3.1.
https://bugs.freedesktop.org/show_bug.cgi?id=98480
So CMAA can use R8 texture, instead of RGBA8.
In addition, CMAA implementation checks R8 support tests, and it slows down GPU
initialization. Remove all unnecessary tests and just check certain extensions.
BUG=535198, 642290
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Review-Url: https://codereview.chromium.org/2693653002
Cr-Commit-Position: refs/heads/master@{#455170}
4 files changed
