GpuServiceImpl: add a GLContext and a GrContext

This CL adds a GLContext and a GrContext in GpuServiceImpl. They are
created when viz::SkiaOutputSurface needs a GrContext to create a SkSurface
for the framebuffer. This CL also creates a SequenceId for
viz::SkiaOutputSurface to play back Skia DDLs on the GPU thread.

This CL is part of CL https://crrev.com/c/947047 which makes
SkiaRenderer use Skia DDL to render frames.

Bug: 824382
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel
Change-Id: I9091fd46cbaafe0ace363bfe63e61b5a0d9fe32d
Reviewed-on: https://chromium-review.googlesource.com/973757
Commit-Queue: Peng Huang <penghuang@chromium.org>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545129}
2 files changed