gl/test: Move some initialization code used in tests to a separate component.

Moving test-code to a separete component, so that adding more test-only
dependencies does not affect non-test code.

BUG=none
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
TBR=jam@ for non-ui/gl/ changes, since trivial #include/gyp-gn updates

Review URL: https://codereview.chromium.org/1238443004

Cr-Commit-Position: refs/heads/master@{#339539}
diff --git a/gpu/BUILD.gn b/gpu/BUILD.gn
index e940614..6e8d96b 100644
--- a/gpu/BUILD.gn
+++ b/gpu/BUILD.gn
@@ -247,6 +247,7 @@
     "//ui/gfx:test_support",
     "//ui/gl",
     "//ui/gl:gl_unittest_utils",
+    "//ui/gl:test_support",
     "//gpu/command_buffer/common:gles2_utils",
     "//gpu/command_buffer/client:gles2_c_lib",
     "//gpu/command_buffer/client:gles2_implementation",