mus Window Server: implement event capture

components/mus/ws/event_dispatcher_delegate.h

Index: components/mus/ws/event_dispatcher_delegate.h
diff --git a/components/mus/ws/event_dispatcher_delegate.h b/components/mus/ws/event_dispatcher_delegate.h
index 5ba2152a43891949ca58c8475f5820ae778fbe54..bc6219d5834f5060ab28811997889e876e771386 100644
--- a/components/mus/ws/event_dispatcher_delegate.h
+++ b/components/mus/ws/event_dispatcher_delegate.h
@@ -22,6 +22,15 @@ class EventDispatcherDelegate {
   virtual void SetFocusedWindowFromEventDispatcher(ServerWindow* window) = 0;
   virtual ServerWindow* GetFocusedWindowForEventDispatcher() = 0;
 
+  // Called when capture should be set on the native display.
+  virtual void SetNativeCapture() = 0;
+  // Called when the native display is having capture released. There is no
+  // longer a ServerWindow holding capture.
+  virtual void ReleaseNativeCapture() = 0;
+  // Called when |window| has lost capture. The native display may still be
+  // holding capture.

[sky, 2016/02/10 23:30:02]

Please add something along the lines of 'delegate should not change native
display capture. ReleaseNativeCapture() is invoked if appropriate.'

[jonross, 2016/02/11 00:26:28]

Done.

+  virtual void OnServerWindowCaptureLost(ServerWindow* window) = 0;
+
   // |in_nonclient_area| is true if the event occurred in the non-client area.
   virtual void DispatchInputEventToWindow(ServerWindow* target,
                                           bool in_nonclient_area,