[Mac] ScopedSendingEvent finds NSApp by itself.

base/chrome_application_mac.h

 // Copyright (c) 2009 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 BASE_CHROME_APPLICATION_MAC_H_
 #define BASE_CHROME_APPLICATION_MAC_H_
 
 #import <AppKit/AppKit.h>
 
 #include "base/basictypes.h"
 
 @interface CrApplication : NSApplication {
  @private
   BOOL handlingSendEvent_;
 }
 @property(readonly,
           getter=isHandlingSendEvent,
           nonatomic) BOOL handlingSendEvent;
 
 + (NSApplication*)sharedApplication;
 @end
 
 namespace chrome_application_mac {
 
 // Controls the state of |handlingSendEvent_| in the event loop so that it is
 // reset properly.
 class ScopedSendingEvent {
  public:
-  explicit ScopedSendingEvent(CrApplication* app);
+  ScopedSendingEvent();
   ~ScopedSendingEvent();
 
  private:
   CrApplication* app_;
   BOOL handling_;
   DISALLOW_COPY_AND_ASSIGN(ScopedSendingEvent);
 };
 
 }  // chrome_application_mac
 
 #endif  // BASE_CHROME_APPLICATION_MAC_H_