[Mac] Inform reference counted objects that hold a weak Browser* when the Browser is being destroye…

chrome/browser/ui/cocoa/tabs/tab_strip_controller.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/ui/cocoa/tabs/tab_strip_controller.h"
 
 #import <QuartzCore/QuartzCore.h>
 
 #include <cmath>
 #include <limits>
@@ skipping 555 matching lines @@
     if (existingTabCount) {
       [self performSelectorOnMainThread:@selector(layoutTabs)
                              withObject:nil
                           waitUntilDone:NO];
     }
   }
   return self;
 }
 
 - (void)dealloc {
+  [self browserWillBeDestroyed];
+  [super dealloc];
+}
+
+- (void)browserWillBeDestroyed {
   [tabStripView_ setController:nil];
 
   if (trackingArea_.get())
     [tabStripView_ removeTrackingArea:trackingArea_.get()];
 
   [newTabButton_ removeTrackingArea:newTabTrackingArea_.get()];
   // Invalidate all closing animations so they don't call back to us after
   // we're gone.
   for (TabController* controller in closingControllers_.get()) {
     NSView* view = [controller view];
     [[[view animationForKey:@"frameOrigin"] delegate] invalidate];
   }
   [[NSNotificationCenter defaultCenter] removeObserver:self];
-  [super dealloc];
+
+  browser_ = nullptr;
 }
 
 + (CGFloat)defaultTabHeight {
   return [TabController defaultTabHeight];
 }
 
 + (CGFloat)defaultLeftIndentForControls {
   // Default indentation leaves enough room so tabs don't overlap with the
   // window controls.
   return 70.0;
@@ skipping 1677 matching lines @@
                     forButtonState:image_button_cell::kHoverStateBackground];
   } else {
     [[newTabButton_ cell] setImage:nil
                     forButtonState:image_button_cell::kDefaultStateBackground];
     [[newTabButton_ cell] setImage:nil
                     forButtonState:image_button_cell::kHoverStateBackground];
   }
 }
 
 @end