Implement hit tests/client area.

ui/aura/mus/window_tree_client.cc

Index: ui/aura/mus/window_tree_client.cc
diff --git a/ui/aura/mus/window_tree_client.cc b/ui/aura/mus/window_tree_client.cc
index a84e1e2f3c97cbfd89d7b88abfb30d4c2cb50f1f..240ca17a06798deb9a11526f7b0715a9b30f7459 100644
--- a/ui/aura/mus/window_tree_client.cc
+++ b/ui/aura/mus/window_tree_client.cc
@@ -1476,6 +1476,23 @@ void WindowTreeClient::OnWindowTreeHostBoundsWillChange(
                                window_tree_host->GetBounds(), bounds);
 }
 
+void WindowTreeClient::OnWindowTreeHostClientAreaWillChange(
+    WindowTreeHostMus* window_tree_host,
+    const gfx::Insets& insets) {
+  SetClientArea(window_tree_host->window(), insets, std::vector<gfx::Rect>());
+}
+
+void WindowTreeClient::OnWindowTreeHostClearHitTestMask(
+    WindowTreeHostMus* window_tree_host) {
+  ClearHitTestMask(window_tree_host->window());
+}
+
+void WindowTreeClient::OnWindowTreeHostHitTestMaskWillChange(
+    WindowTreeHostMus* window_tree_host,
+    const gfx::Rect& mask_rect) {
+  SetHitTestMask(window_tree_host->window(), mask_rect);
+}
+
 std::unique_ptr<WindowPortMus> WindowTreeClient::CreateWindowPortForTopLevel() {
   std::unique_ptr<WindowPortMus> window_port =
       base::MakeUnique<WindowPortMus>(this, WindowMusType::TOP_LEVEL);