Fix up compositor mocking.

ui/gfx/compositor/test_compositor.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/compositor/test_compositor.h"
 
 #include "ui/gfx/compositor/test_texture.h"
 
 namespace ui {
 
@@ skipping 34 matching lines @@
 void TestCompositor::DrawTree() {
 #if !defined(USE_WEBKIT_COMPOSITOR)
   Compositor::DrawTree();
 #endif
 }
 
 ui::Compositor* TestCompositor::Create(ui::CompositorDelegate* owner) {
   return new ui::TestCompositor(owner);
 }
 
+void TestCompositor::SetupTestCompositor() {
+#if defined(VIEWS_COMPOSITOR)
+  ui::Compositor::set_compositor_factory_for_testing(
+      ui::TestCompositor::Create);
+#endif
+}
+
 void TestCompositor::OnWidgetSizeChanged() {
 }
 
 }  // namespace ui