Don't try to show the Mac password bubble on an inactive tab.

chrome/browser/ui/cocoa/passwords/manage_passwords_bubble_cocoa.mm

 // Copyright 2014 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/passwords/manage_passwords_bubble_cocoa.h"
 
 #include "base/mac/scoped_block.h"
 #include "chrome/browser/ui/browser_dialogs.h"
 #include "chrome/browser/ui/browser_finder.h"
 #import "chrome/browser/ui/cocoa/browser_window_controller.h"
@@ skipping 33 matching lines @@
   ManagePasswordsBubbleCocoa* instance = ManagePasswordsBubbleCocoa::instance();
   if (instance && (instance->webContents_ != webContents)) {
     // The bubble is currently shown for some other tab. We should close it now
     // and open for |webContents|.
     instance->Close();
   }
 
   ManagePasswordsUIController* controller =
       ManagePasswordsUIController::FromWebContents(webContents);
   NSWindow* window = webContents->GetTopLevelNativeWindow();
+  if (!window) {
+    // The tab isn't active right now.
+    return;
+  }
   BrowserWindowController* bwc =
       [BrowserWindowController browserWindowControllerForWindow:window];
   ManagePasswordsBubbleCocoa::ShowBubble(
       webContents,
       password_manager::ui::IsAutomaticDisplayState(controller->state())
           ? ManagePasswordsBubble::AUTOMATIC
           : ManagePasswordsBubble::USER_ACTION,
       [bwc locationBarBridge]->manage_passwords_decoration()->icon());
 }
 }  // namespace chrome
@@ skipping 59 matching lines @@
 
 // static
 void ManagePasswordsBubbleCocoa::ShowBubble(content::WebContents* webContents,
                                             DisplayReason displayReason,
                                             ManagePasswordsIcon* icon) {
   if (bubble_)
     return;
   bubble_ = new ManagePasswordsBubbleCocoa(webContents, displayReason, icon);
   bubble_->Show();
 }