mac: Fix copying from the Omnibox.

chrome/browser/ui/cocoa/omnibox/omnibox_view_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.
 
 #include "chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.h"
 
 #include <Carbon/Carbon.h>  // kVK_Return
 
 #include "base/mac/foundation_util.h"
 #include "base/metrics/histogram.h"
@@ skipping 939 matching lines @@
   NSString* nstext = base::SysUTF16ToNSString(text);
   if (write_url) {
     return ui::ClipboardUtil::PasteboardItemFromUrl(
         base::SysUTF8ToNSString(url.spec()), nstext);
   } else {
     return ui::ClipboardUtil::PasteboardItemFromString(nstext);
   }
 }
 
 void OmniboxViewMac::CopyToPasteboard(NSPasteboard* pboard) {
+  [pboard clearContents];
   base::scoped_nsobject<NSPasteboardItem> item(CreatePasteboardItem());
   [pboard writeObjects:@[ item.get() ]];
 }
 
 void OmniboxViewMac::ShowURL() {
   DCHECK(ShouldEnableShowURL());
   OmniboxView::ShowURL();
 }
 
 void OmniboxViewMac::OnPaste() {
@@ skipping 136 matching lines @@
 
 NSUInteger OmniboxViewMac::GetTextLength() const {
   return [field_ currentEditor] ?  [[[field_ currentEditor] string] length] :
                                    [[field_ stringValue] length];
 }
 
 bool OmniboxViewMac::IsCaretAtEnd() const {
   const NSRange selection = GetSelectedRange();
   return NSMaxRange(selection) == GetTextLength();
 }