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We used to fake out the Gpu::Capabilities in TestInProcessContextProvider with some custom logic.
This logic appears to be redundant with the actual capabilities we can get from the real context.
Additionally, as this code is used in pixel tests, having fake capabilities that mismatch with the
real capabilities seems risky, so if the real caps are working it feels like we should use them.

Also cleans up some other unused code.

R=enne

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: I1bf82739387a358e95372efb1dac571d7ed15cbe
Reviewed-on: https://chromium-review.googlesource.com/957315Reviewed-by: enne <enne@chromium.org>
Commit-Queue: Eric Karl <ericrk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542257}