Use TestGpuServiceHolder in more tests.

Change InProcessContextProvider to use TestGpuServiceHolder instead of
GetTestGpuThreadHolder(). Both provide a working GPU thread but
TestGpuServiceProvider has a working GpuServiceImpl which is required
for SkiaRenderer.

A few test suites need mojo initialized for this to work.
NativeWindowOcclusionTrackerTest is a special case of tests that aren't
browser test based and don't get mojo initialized. We can safely
initialize mojo at the start of each test as all interactive_ui_tests
run in their own process.

exo_unittests had a problem where GL was shutdown before the GPU
service. Resetting the GPU service at the end of each test fixes this.

Bug: 956144
Change-Id: I0cba4b892e81f50e84b13a20324f7eacd5f3a45c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1632913
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Jonathan Backer <backer@chromium.org>
Commit-Queue: kylechar <kylechar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#675619}

• components/exo/test/DEPS[Added - diff]
• components/exo/test/run_all_unittests.cc[diff]
• ui/aura/BUILD.gn[diff]
• ui/aura/DEPS[diff]
• ui/aura/native_window_occlusion_tracker_win_interactive_test.cc[diff]
• ui/compositor/test/in_process_context_provider.cc[diff]
• ui/message_center/BUILD.gn[diff]
• ui/message_center/test/DEPS[diff]
• ui/message_center/test/run_all_unittests.cc[diff]