Add CONTEXT_TYPE_OPENGLES2_PEPPER

Adds a new context type for Pepper GL contexts. This allows us to
fine tune driver bug workarounds for pepper vs. non-pepper contexts.

Currently used to disable the Intel MSAA blacklist on pepper contexts,
as it should be up to the app whether to use MSAA.

BUG=527565
CQ_INCLUDE_TRYBOTS=tryserver.chromium.win:win_optional_gpu_tests_rel;tryserver.chromium.mac:mac_optional_gpu_tests_rel

Review URL: https://codereview.chromium.org/1781093002

Cr-Commit-Position: refs/heads/master@{#382097}
11 files changed