Fix crash when closing tab with an open http auth sheet.

chrome/browser/login_prompt_mac.mm

 // Copyright (c) 2009 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/login_prompt.h"
 #import "chrome/browser/login_prompt_mac.h"
 
 #include "app/l10n_util.h"
 #include "base/mac_util.h"
 #include "base/message_loop.h"
@@ skipping 44 matching lines @@
       NOTREACHED();
     }
   }
 
   virtual ~LoginHandlerMac() {
     if (login_model_)
       login_model_->SetObserver(NULL);
   }
 
   void SetModel(LoginModel* model) {
+    if (login_model_)
+      login_model_->SetObserver(NULL);
     login_model_ = model;
     if (login_model_)
       login_model_->SetObserver(this);
   }
 
   // LoginModelObserver implementation.
   virtual void OnAutofillDataAvailable(const std::wstring& username,
                                        const std::wstring& password) {
     [sheet_controller_ autofillLogin:base::SysWideToNSString(username)
                             password:base::SysWideToNSString(password)];
@@ skipping 82 matching lines @@
 
   // Overridden from ConstrainedWindowMacDelegate:
   virtual void DeleteDelegate() {
     if (!WasAuthHandled(true)) {
       request_loop_->PostTask(FROM_HERE, NewRunnableMethod(
           this, &LoginHandlerMac::CancelAuthDeferred));
       ui_loop_->PostTask(FROM_HERE, NewRunnableMethod(
           this, &LoginHandlerMac::SendNotifications));
     }
 
+    // Close sheet if it's still open, as required by
+    // ConstrainedWindowMacDelegate.
+    DCHECK(MessageLoop::current() == ui_loop_);
+    if (is_sheet_open())
+      [NSApp endSheet:sheet()];
+
+    SetModel(NULL);
+
     // Delete this object once all InvokeLaters have been called.
     request_loop_->ReleaseSoon(FROM_HERE, this);
   }
 
   void OnLoginPressed(const std::wstring& username,
                       const std::wstring& password) {
     DCHECK(MessageLoop::current() == ui_loop_);
     SetAuth(username, password);
   }
 
@@ skipping 25 matching lines @@
       // Verify that CancelAuth does destroy the request via our delegate.
       DCHECK(request_ != NULL);
       ResetLoginHandlerForRequest(request_);
     }
   }
 
   // Closes the view_contents from the UI loop.
   void CloseContentsDeferred() {
     DCHECK(MessageLoop::current() == ui_loop_);
 
-    // Close sheet if it's still open, as required by
-    // ConstrainedWindowMacDelegate.
-    if (is_sheet_open())
-      [NSApp endSheet:sheet()];
-
     // The hosting ConstrainedWindow may have been freed.
     if (dialog_)
       dialog_->CloseConstrainedWindow();
   }
 
   // Returns whether authentication had been handled (SetAuth or CancelAuth).
   // If |set_handled| is true, it will mark authentication as handled.
   bool WasAuthHandled(bool set_handled) {
     AutoLock lock(handled_auth_lock_);
     bool was_handled = handled_auth_;
@@ skipping 108 matching lines @@
 
 - (void)autofillLogin:(NSString*)login password:(NSString*)password {
   if ([[nameField_ stringValue] length] == 0) {
     [nameField_ setStringValue:login];
     [passwordField_ setStringValue:password];
     [nameField_ selectText:self];
   }
 }
 
 @end