Rewrite scoped_ptr<T>(NULL) to use the default ctor.

chrome/browser/chrome_browser_application_mac.mm

 // Copyright (c) 2012 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.
 
 #import "chrome/browser/chrome_browser_application_mac.h"
 
 #import "base/auto_reset.h"
 #include "base/debug/crash_logging.h"
 #include "base/debug/stack_trace.h"
 #import "base/logging.h"
@@ skipping 388 matching lines @@
   // exceptions and Chromium cannot fix them.  This provides a way to
   // work around those on a spot basis.
   bool enableNSExceptions = false;
 
   // http://crbug.com/80686 , an Epson printer driver.
   if (anAction == @selector(selectPDE:)) {
     enableNSExceptions = true;
   }
 
   // Minimize the window by keeping this close to the super call.
-  scoped_ptr<base::mac::ScopedNSExceptionEnabler> enabler(NULL);
+  scoped_ptr<base::mac::ScopedNSExceptionEnabler> enabler;
   if (enableNSExceptions)
     enabler.reset(new base::mac::ScopedNSExceptionEnabler());
   return [super sendAction:anAction to:aTarget from:sender];
 }
 
 - (BOOL)isHandlingSendEvent {
   return handlingSendEvent_;
 }
 
 - (void)setHandlingSendEvent:(BOOL)handlingSendEvent {
@@ skipping 151 matching lines @@
   std::vector<NSWindow*>::iterator window_iterator =
       std::find(previousKeyWindows_.begin(),
                 previousKeyWindows_.end(),
                 window);
   if (window_iterator != previousKeyWindows_.end()) {
     previousKeyWindows_.erase(window_iterator);
   }
 }
 
 @end