Safebrowsing: Fix crash if DownloadItem is destroyed before history check.

chrome/browser/safe_browsing/download_protection_service.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/safe_browsing/download_protection_service.h"
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/format_macros.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 626 matching lines @@
         BrowserThread::UI,
         FROM_HERE,
         base::Bind(&CheckClientDownloadRequest::GetTabRedirects, this));
 #else
     PostFinishTask(UNKNOWN, REASON_OS_NOT_SUPPORTED);
 #endif
   }
 
   void GetTabRedirects() {
     DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+    if (!service_)
+      return;
+
     if (!tab_url_.is_valid()) {
       SendRequest();
       return;
     }
 
     Profile* profile = Profile::FromBrowserContext(item_->GetBrowserContext());
     HistoryService* history =
         HistoryServiceFactory::GetForProfile(profile, Profile::EXPLICIT_ACCESS);
     if (!history) {
       SendRequest();
       return;
     }
 
     history->QueryRedirectsTo(
         tab_url_,
         base::Bind(&CheckClientDownloadRequest::OnGotTabRedirects,
                    base::Unretained(this),
                    tab_url_),
         &request_tracker_);
   }
 
   void OnGotTabRedirects(const GURL& url,
                          const history::RedirectList* redirect_list) {
     DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
     DCHECK_EQ(url, tab_url_);
+    if (!service_)
+      return;
 
     if (!redirect_list->empty()) {
       tab_redirects_.insert(
           tab_redirects_.end(), redirect_list->rbegin(), redirect_list->rend());
     }
 
     SendRequest();
   }
 
   void SendRequest() {
@@ skipping 418 matching lines @@
 GURL DownloadProtectionService::GetDownloadRequestUrl() {
   GURL url(kDownloadRequestUrl);
   std::string api_key = google_apis::GetAPIKey();
   if (!api_key.empty())
     url = url.Resolve("?key=" + net::EscapeQueryParamValue(api_key, true));
 
   return url;
 }
 
 }  // namespace safe_browsing