Allow new zoom bubble to override current one.

chrome/browser/ui/cocoa/location_bar/zoom_decoration.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/location_bar/zoom_decoration.h"
 
 #include "base/strings/string16.h"
 #include "base/strings/string_number_conversions.h"
 #include "chrome/app/chrome_command_ids.h"
 #import "chrome/browser/ui/cocoa/location_bar/autocomplete_text_field.h"
@@ skipping 30 matching lines @@
       l10n_util::GetNSStringFWithFixup(IDS_TOOLTIP_ZOOM, zoom_percent);
 
   if (IsVisible() && [tooltip_ isEqualToString:zoom_string])
     return false;
 
   ShowAndUpdateUI(zoom_controller, zoom_string);
   return true;
 }
 
 void ZoomDecoration::ShowBubble(BOOL auto_close) {
-  if (bubble_)
-    return;
-
   content::WebContents* web_contents = owner_->GetWebContents();
   if (!web_contents)
     return;
 
   // Get the frame of the decoration.
   AutocompleteTextField* field = owner_->GetAutocompleteTextField();
   const NSRect frame =
       [[field cell] frameForDecoration:this inFrame:[field bounds]];
 
   // Find point for bubble's arrow in screen coordinates.
   NSPoint anchor = GetBubblePointInFrame(frame);
   anchor = [field convertPoint:anchor toView:nil];
   anchor = [[field window] convertBaseToScreen:anchor];
 
   bubble_ = [[ZoomBubbleController alloc] initWithParentWindow:[field window]

[sky, 2015/01/22 20:40:56]

This seems like you're going to end up with two bubbles? Is that right? Wouldn't
it be better to change the existing bubble?

                                                       delegate:this];
   [bubble_ showAnchoredAt:anchor autoClose:auto_close];
 }
 
 void ZoomDecoration::CloseBubble() {
   [bubble_ close];
 }
 
 void ZoomDecoration::HideUI() {
   [bubble_ close];
@@ skipping 62 matching lines @@
   bubble_ = nil;
 
   // If the page is at default zoom then hiding the zoom decoration
   // was suppressed while the bubble was open. Now that the bubble is
   // closed the decoration can be hidden.
   if (IsAtDefaultZoom() && IsVisible()) {
     SetVisible(false);
     owner_->OnDecorationsChanged();
   }
 }