Don't try to use ManagePasswordsBubbleModel if the password bubble was closed.

chrome/browser/ui/cocoa/passwords/passwords_bubble_controller_unittest.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.
 
 #include "chrome/browser/ui/cocoa/passwords/passwords_bubble_controller.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/compiler_specific.h"
 #include "base/mac/foundation_util.h"
@@ skipping 63 matching lines @@
             [[controller() currentController] class]);
 }
 
 TEST_F(ManagePasswordsBubbleControllerTest,
        PendingStateShouldHaveUpdatePendingView) {
   SetUpUpdatePendingState(false);
   EXPECT_EQ([UpdatePendingPasswordViewController class],
             [[controller() currentController] class]);
 }
 
+TEST_F(ManagePasswordsBubbleControllerTest, ClearModelOnClose) {
+  SetUpUpdatePendingState(false);
+  EXPECT_TRUE(controller().model);
+  [controller() close];
+  EXPECT_FALSE(controller().model);
+}
+
 }  // namespace