mus: Implement Window Server Capture

components/mus/ws/window_tree_host_impl.h

Index: components/mus/ws/window_tree_host_impl.h
diff --git a/components/mus/ws/window_tree_host_impl.h b/components/mus/ws/window_tree_host_impl.h
index dd7f00323b892af5e366adb9bc9fd53092f7137c..d3d1b758a216cfe3e401261e96c21cd1869670e8 100644
--- a/components/mus/ws/window_tree_host_impl.h
+++ b/components/mus/ws/window_tree_host_impl.h
@@ -80,6 +80,9 @@ class WindowTreeHostImpl : public DisplayManagerDelegate,
   ServerWindow* root_window() { return root_.get(); }
   const ServerWindow* root_window() const { return root_.get(); }
 
+  void SetCapture(ServerWindow* window);
+  void ReleaseCapture(ServerWindow* window);
+
   void SetFocusedWindow(ServerWindow* window);
   ServerWindow* GetFocusedWindow();
   void DestroyFocusController();
@@ -88,6 +91,13 @@ class WindowTreeHostImpl : public DisplayManagerDelegate,
                             const ui::TextInputState& state);
   void SetImeVisibility(ServerWindow* window, bool visible);
 
+  // Returns the window that has captured input.
+  ServerWindow* GetCaptureWindow() {
+    return event_dispatcher_.capture_window();
+  }
+  const ServerWindow* GetCaptureWindow() const {
+    return event_dispatcher_.capture_window();
+  }
   // WindowTreeHost:
   void SetSize(mojo::SizePtr size) override;
   void SetTitle(const mojo::String& title) override;
@@ -101,6 +111,7 @@ class WindowTreeHostImpl : public DisplayManagerDelegate,
   // DisplayManagerDelegate:
   ServerWindow* GetRootWindow() override;
   void OnEvent(mojom::EventPtr event) override;
+  void OnLostCapture() override;
   void OnDisplayClosed() override;
   void OnViewportMetricsChanged(
       const mojom::ViewportMetrics& old_metrics,
@@ -116,6 +127,7 @@ class WindowTreeHostImpl : public DisplayManagerDelegate,
   void OnAccelerator(uint32_t accelerator_id, mojom::EventPtr event) override;
   void SetFocusedWindowFromEventDispatcher(ServerWindow* window) override;
   ServerWindow* GetFocusedWindowForEventDispatcher() override;
+  void OnLostCapture(ServerWindow* window) override;
   void DispatchInputEventToWindow(ServerWindow* target,
                                   bool in_nonclient_area,
                                   mojom::EventPtr event) override;