MacViews: Fix failing mouse capture unittests.

ui/views/cocoa/cocoa_mouse_capture_delegate.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_VIEWS_COCOA_COCOA_MOUSE_CAPTURE_DELEGATE_H_
 #define UI_VIEWS_COCOA_COCOA_MOUSE_CAPTURE_DELEGATE_H_
 
 @class NSEvent;
+@class NSWindow;
 
 namespace views {
 
 // Delegate for receiving captured events from a CocoaMouseCapture.
 class CocoaMouseCaptureDelegate {
  public:
   // Called when an event has been captured. This may be an event local to the
   // application, or a global event (sent to another application). If it is a
   // local event, regular event handling will be suppressed.
   virtual void PostCapturedEvent(NSEvent* event) = 0;
 
   // Called once. When another window acquires capture, or when the
   // CocoaMouseCapture is destroyed.
   virtual void OnMouseCaptureLost() = 0;
+
+  // Returns the associated NSWindow.
+  virtual NSWindow* GetWindow() const = 0;
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_COCOA_COCOA_MOUSE_CAPTURE_DELEGATE_H_