Fix the crash that could occur when the window is closed while web contents drag is in progress.

content/browser/web_contents/web_contents_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.
 
 #import <Carbon/Carbon.h>
 
 #import "content/browser/web_contents/web_contents_view_mac.h"
 
 #include <string>
 
@@ skipping 232 matching lines @@
     // TODO(shess): If location-bar gets focus by default, this will
     // select-all in the field.  If there was a specific selection in
     // the field when we navigated away from it, we should restore
     // that selection.
     SetInitialFocus();
   }
 
   focus_tracker_.reset(nil);
 }
 
-bool WebContentsViewMac::IsDoingDrag() const {
-  return false;
-}
-
-void WebContentsViewMac::CancelDragAndCloseTab() {
-}
-
 WebDropData* WebContentsViewMac::GetDropData() const {
   return [cocoa_view_ dropData];
 }
 
 void WebContentsViewMac::UpdateDragCursor(WebDragOperation operation) {
   [cocoa_view_ setCurrentDragOperation: operation];
 }
 
 void WebContentsViewMac::GotFocus() {
   // This is only used in the views FocusManager stuff but it bleeds through
@@ skipping 238 matching lines @@
 
 - (void)cancelDeferredClose {
   SEL aSel = @selector(closeTabAfterEvent);
   [NSObject cancelPreviousPerformRequestsWithTarget:self
                                            selector:aSel
                                              object:nil];
 }
 
 - (void)clearWebContentsView {
   webContentsView_ = NULL;
+  [dragSource_ clearWebContentsView];
 }
 
 - (void)closeTabAfterEvent {
   webContentsView_->CloseTab();
 }
 
 - (void)viewDidBecomeFirstResponder:(NSNotification*)notification {
   NSView* view = [notification object];
   if (![[self subviews] containsObject:view])
     return;
 
   NSSelectionDirection direction =
       [[[notification userInfo] objectForKey:kSelectionDirection]
         unsignedIntegerValue];
   if (direction == NSDirectSelection)
     return;
 
   [self webContents]->
       FocusThroughTabTraversal(direction == NSSelectingPrevious);
 }
 
 @end