ui: No more TestCompositor. Use NullDraw contexts in unit tests.

ui/compositor/test/context_factories_for_test.h

Index: ui/compositor/test/context_factories_for_test.h
diff --git a/ui/compositor/test/context_factories_for_test.h b/ui/compositor/test/context_factories_for_test.h
index a2b314f067b68d37c2de94d849a02f3fd5a0da66..ae4e51e7bc2d03fd77f4d2aa5070653627f0a85e 100644
--- a/ui/compositor/test/context_factories_for_test.h
+++ b/ui/compositor/test/context_factories_for_test.h
@@ -7,10 +7,10 @@ namespace ui {
 // Set up the compositor ContextFactory for a test environment. Unit tests
 // that do not have a full content environment need to call this before
 // initializing the Compositor.
-// Some tests expect pixel output, and they should pass false for
-// |allow_test_contexts|. Most unit tests should pass true. Once this has been
+// Some tests expect pixel output, and they should pass true for
+// |enable_pixel_output|. Most unit tests should pass false. Once this has been
 // called, the caller must call TerminateContextFactoryForTests() to clean up.
-void InitializeContextFactoryForTests(bool allow_test_contexts);
+void InitializeContextFactoryForTests(bool enable_pixel_output);
 void TerminateContextFactoryForTests();
 
 }  // namespace ui