Mac: Fix crash while dragging a tab alone in a window.

chrome/browser/cocoa/tab_strip_controller.mm

 // 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.
 
 #import "chrome/browser/cocoa/tab_strip_controller.h"
 
 #include "app/l10n_util.h"
 #include "app/resource_bundle.h"
 #include "base/mac_util.h"
 #include "base/sys_string_conversions.h"
@@ skipping 613 matching lines @@
   // Release the tab contents controller so those views get destroyed. This
   // will remove all the tab content Cocoa views from the hierarchy. A
   // subsequent "select tab" notification will follow from the model. To
   // tell us what to swap in in its absence.
   [tabContentsArray_ removeObjectAtIndex:index];
 
   // Remove the |index|th view from the tab strip
   NSView* tab = [self viewAtIndex:index];
   [tab removeFromSuperview];
 
+  // Clear the tab controller's target.
+  // TODO(viettrungluu): [crbug.com/23829] Find a better way to handle the tab
+  // controller's target.
+  TabController* tabController = [tabArray_ objectAtIndex:index];
+  [tabController setTarget:nil];
+
   if ([hoveredTab_ isEqual:tab]) {
     hoveredTab_ = nil;
   }
 
   NSValue *identifier = [NSValue valueWithPointer:tab];
   [targetFrames_ removeObjectForKey:identifier];
 
   // Once we're totally done with the tab, delete its controller
   [tabArray_ removeObjectAtIndex:index];
 
@@ skipping 335 matching lines @@
   BrowserWindowController* controller =
       (BrowserWindowController*)[[switchView_ window] windowController];
   DCHECK(index >= 0);
   if (index >= 0) {
     [controller setTab:[self viewAtIndex:index] isDraggable:YES];
   }
 }
 
 
 @end