We have a problem in the process on destroying WebContentsImpl because

chrome/browser/download/download_request_limiter.cc

 // 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.
 
 #include "chrome/browser/download/download_request_limiter.h"
 
 #include "base/bind.h"
 #include "base/stl_util.h"
 #include "chrome/browser/content_settings/host_content_settings_map.h"
 #include "chrome/browser/content_settings/tab_specific_content_settings.h"
@@ skipping 92 matching lines @@
   // DOWNLOADS_NOT_ALLOWED is functionally equivalent to PROMPT_BEFORE_DOWNLOAD.
   if ((status_ != DownloadRequestLimiter::ALLOW_ALL_DOWNLOADS) &&
       (!promptable ||
        (status_ != DownloadRequestLimiter::DOWNLOADS_NOT_ALLOWED))) {
     // Revert to default status.
     host_->Remove(this, web_contents());
     // WARNING: We've been deleted.
   }
 }
 
-void DownloadRequestLimiter::TabDownloadState::WebContentsDestroyed(
-    content::WebContents* web_contents) {
+void DownloadRequestLimiter::TabDownloadState::WebContentsDestroyed() {
   // Tab closed, no need to handle closing the dialog as it's owned by the
   // WebContents.
 
   NotifyCallbacks(false);
-  // Note that web_contents() is NULL at this point.
-  host_->Remove(this, web_contents);
+  host_->Remove(this, web_contents());
   // WARNING: We've been deleted.
 }
 
 void DownloadRequestLimiter::TabDownloadState::PromptUserForDownload(
     const DownloadRequestLimiter::Callback& callback) {
   callbacks_.push_back(callback);
   DCHECK(web_contents_);
   if (is_showing_prompt())
     return;
 
@@ skipping 331 matching lines @@
   BrowserThread::PostTask(
       BrowserThread::IO, FROM_HERE, base::Bind(callback, allow));
 }
 
 void DownloadRequestLimiter::Remove(TabDownloadState* state,
                                     content::WebContents* contents) {
   DCHECK(ContainsKey(state_map_, contents));
   state_map_.erase(contents);
   delete state;
 }