[OSX] Allow one zoom bubble to override another.

chrome/browser/ui/cocoa/browser/zoom_bubble_controller.mm

 // Copyright (c) 2013 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/browser/zoom_bubble_controller.h"
 
 #include "base/mac/foundation_util.h"
 #include "base/strings/string_number_conversions.h"
 #import "chrome/browser/ui/cocoa/info_bubble_view.h"
 #import "chrome/browser/ui/cocoa/info_bubble_window.h"
@@ skipping 57 matching lines @@
 namespace chrome {
 
 void SetZoomBubbleAutoCloseDelayForTesting(NSTimeInterval time_interval) {
   gAutoCloseDelay = time_interval;
 }
 
 }  // namespace chrome
 
 @implementation ZoomBubbleController
 
+@synthesize delegate = delegate_;
+
 - (id)initWithParentWindow:(NSWindow*)parentWindow
                   delegate:(ZoomBubbleControllerDelegate*)delegate {
   base::scoped_nsobject<InfoBubbleWindow> window(
       [[InfoBubbleWindow alloc] initWithContentRect:NSMakeRect(0, 0, 200, 100)
                                           styleMask:NSBorderlessWindowMask
                                             backing:NSBackingStoreBuffered
                                               defer:NO]);
   if ((self = [super initWithWindow:window
                        parentWindow:parentWindow
                          anchoredAt:NSZeroPoint])) {
@@ skipping 31 matching lines @@
       : info_bubble::kAnimateNone];
 
   self.anchorPoint = anchorPoint;
   [self showWindow:nil];
 
   autoClose_ = autoClose;
   [self updateAutoCloseTimer];
 }
 
 - (void)onZoomChanged {
+  // |delegate_| may be set null by this object's owner.
+  if (!delegate_)
+    return;
+
   // TODO(shess): It may be appropriate to close the window if
   // |contents| or |zoomController| are NULL.  But they can be NULL in
   // tests.
 
   content::WebContents* contents = delegate_->GetWebContents();
   if (!contents)
     return;
 
   ui_zoom::ZoomController* zoomController =
       ui_zoom::ZoomController::FromWebContents(contents);
@@ skipping 23 matching lines @@
 }
 
 - (void)closeWithoutAnimation {
   InfoBubbleWindow* window =
       base::mac::ObjCCastStrict<InfoBubbleWindow>([self window]);
   [window setAllowedAnimations:info_bubble::kAnimateNone];
   [self close];
 }
 
 - (void)windowWillClose:(NSNotification*)notification {
-  delegate_->OnClose();
-  delegate_ = NULL;
+  // |delegate_| may be set null by this object's owner.
+  if (delegate_) {
+    delegate_->OnClose();
+    delegate_ = NULL;
+  }
   [NSObject cancelPreviousPerformRequestsWithTarget:self
                                            selector:@selector(autoCloseBubble)
                                              object:nil];
   [super windowWillClose:notification];
 }
 
 - (void)mouseEntered:(NSEvent*)theEvent {
   isMouseInside_ = YES;
   [self updateAutoCloseTimer];
 }
@@ skipping 157 matching lines @@
                           range:NSMakeRange(0, [title length])];
     title = selectedTitle.autorelease();
   }
 
   [[self cell] drawTitle:title
                withFrame:bounds
                   inView:self];
 }
 
 @end