Mus: Fixes rendering of transparent containers.

components/mus/ws/test_utils.h

Index: components/mus/ws/test_utils.h
diff --git a/components/mus/ws/test_utils.h b/components/mus/ws/test_utils.h
index 19cb43215c0baa0fd70c3bcf27f6bb3a3beb409c..2c88847f02aad29d1dfb86b719b3507738086703 100644
--- a/components/mus/ws/test_utils.h
+++ b/components/mus/ws/test_utils.h
@@ -216,6 +216,30 @@ class TestPlatformDisplayFactory : public PlatformDisplayFactory {
 
 // -----------------------------------------------------------------------------
 
+// A stub implementation of PlatformDisplayDelegate containing a root
+// ServerWindow.
+class TestPlatformDisplayDelegate : public PlatformDisplayDelegate {
+ public:
+  TestPlatformDisplayDelegate(std::unique_ptr<ServerWindow> root);

[sky, 2016/06/27 15:17:08]

explicit

[mfomitchev, 2016/06/30 22:06:03]

Done.

+  ~TestPlatformDisplayDelegate() override;
+
+  // PlatformDisplayDelegate:
+  ServerWindow* GetRootWindow() override;
+  void OnDisplayClosed() override {}
+  void OnEvent(const ui::Event& event) override {}
+  void OnNativeCaptureLost() override {}
+  void OnViewportMetricsChanged(const ViewportMetrics& old_metrics,
+                                const ViewportMetrics& new_metrics) override {}
+  void OnCompositorFrameDrawn() override {}
+
+ private:
+  std::unique_ptr<ServerWindow> root_;
+
+  DISALLOW_COPY_AND_ASSIGN(TestPlatformDisplayDelegate);
+};
+
+// -----------------------------------------------------------------------------
+
 class TestWindowManager : public mojom::WindowManager {
  public:
   TestWindowManager()