gpu: Clarify the sized texture format is available only if ES3 context or immutable texture is supported.

This clarification makes it possible that gles2 decoder tracks true internal format of immutable texture. So this CL removes internal_format hack in GLES2DecoderImpl::TexStorageImpl()

In addition, it makes CMAA skip redundant copy path because CMAA can know true internal format.

BUG=535198
CQ_INCLUDE_TRYBOTS=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/2117183006
Cr-Commit-Position: refs/heads/master@{#425684}
7 files changed