chromeos: enables more of non-fake cc for CopyOutputRequest to work

Specifically the following:
. TestContextProvider now uses
  skia_bindings::GrContextForGLES2Interface, without this skia doesn't
  use the right context and produces ids that aren't expected.
. Converts Ash to use TestLayerTreeFrameSinkClient vs
  FakeContextFactory. TestLayerTreeFrameSinkClient seems closer to
  what these tests need vs FakeContextFactory.

BUG=734811
TEST=test only changes

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I4f3d7a432d7f23a9e1e243d045846949b52c51fc
Reviewed-on: https://chromium-review.googlesource.com/550587
Commit-Queue: Scott Violet <[email protected]>
Reviewed-by: Eric Karl <[email protected]>
Cr-Commit-Position: refs/heads/master@{#486789}
diff --git a/components/exo/BUILD.gn b/components/exo/BUILD.gn
index a496d19d..8a712ba 100644
--- a/components/exo/BUILD.gn
+++ b/components/exo/BUILD.gn
@@ -183,6 +183,8 @@
     "//ash/test:test_support_without_content",
     "//base",
     "//base/test:test_support",
+    "//cc:test_support",
+    "//components/viz/test:test_support",
     "//device/gamepad:test_helpers",
     "//mojo/edk/embedder:headers",
     "//testing/gtest",