WebGL: tex(Sub)Image(2D|3D) texImageSource support for RGB10_A2 textures.

See: https://github.com/KhronosGroup/WebGL/issues/2274

BUG=714240
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/2821363003
Cr-Commit-Position: refs/heads/master@{#468257}
4 files changed