Use a mocked compositor for unit tests

ui/gfx/compositor/compositor_test_support.cc

Index: ui/gfx/compositor/compositor_test_support.cc
diff --git a/ui/gfx/compositor/compositor_test_support.cc b/ui/gfx/compositor/compositor_test_support.cc
index e72bd0c8204bc5290b1077dbaab1144aa055e212..d9e88e2c5d5249fc52b08ae51e4ade3662877b60 100644
--- a/ui/gfx/compositor/compositor_test_support.cc
+++ b/ui/gfx/compositor/compositor_test_support.cc
@@ -9,6 +9,11 @@
 #include "webkit/glue/webkitplatformsupport_impl.h"
 #endif
 
+#if defined(VIEWS_COMPOSITOR)
+#include "ui/gfx/compositor/compositor.h"
+#include "ui/gfx/compositor/test_compositor.h"
+#endif
+
 namespace ui {
 
 #if defined(USE_WEBKIT_COMPOSITOR)
@@ -32,4 +37,19 @@ void CompositorTestSupport::Terminate() {
 #endif
 }
 
+void CompositorTestSupport::SetupMockCompositor() {
+#if defined(USE_WEBKIT_COMPOSITOR)
+  // TODO(backer): We've got dependencies in Layer that require
+  // WebKit support even though we're mocking the Compositor. We
+  // would ideally mock out these unnecessary dependencies as well.
+  DCHECK(g_webkit_support);
+#endif
+
+#if defined(VIEWS_COMPOSITOR)
+  // Use a mock compositor that noops draws.
+  ui::Compositor::set_compositor_factory_for_testing(
+      ui::TestCompositor::Create);
+#endif
+}
+
 }  // namespace ui