Implement hit tests/client area.

ui/aura/mus/window_tree_client.h

Index: ui/aura/mus/window_tree_client.h
diff --git a/ui/aura/mus/window_tree_client.h b/ui/aura/mus/window_tree_client.h
index f9835fe486dd0e8548e9a172993238e68ab08af7..1e47dcc41f132f3616e098c07af2b02cef879a13 100644
--- a/ui/aura/mus/window_tree_client.h
+++ b/ui/aura/mus/window_tree_client.h
@@ -406,6 +406,13 @@ class AURA_EXPORT WindowTreeClient
   // Overriden from WindowTreeHostMusDelegate:
   void OnWindowTreeHostBoundsWillChange(WindowTreeHostMus* window_tree_host,
                                         const gfx::Rect& bounds) override;
+  void OnWindowTreeHostClientAreaWillChange(WindowTreeHostMus* window_tree_host,
+                                            const gfx::Insets& insets) override;
+  void OnWindowTreeHostClearHitTestMask(
+      WindowTreeHostMus* window_tree_host) override;
+  void OnWindowTreeHostHitTestMaskWillChange(
+      WindowTreeHostMus* window_tree_host,
+      const gfx::Rect& mask_rect) override;
   std::unique_ptr<WindowPortMus> CreateWindowPortForTopLevel() override;
   void OnWindowTreeHostCreated(WindowTreeHostMus* window_tree_host) override;