Fix possible crash when HostZoomMap is NULL

content/browser/resource_context_impl.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 "content/browser/resource_context_impl.h"
 
 #include "base/logging.h"
 #include "content/browser/fileapi/chrome_blob_storage_context.h"
 #include "content/browser/host_zoom_map_impl.h"
 #include "content/browser/loader/resource_dispatcher_host_impl.h"
@@ skipping 76 matching lines @@
 
 StreamContext* GetStreamContextForResourceContext(
     ResourceContext* resource_context) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   return UserDataAdapter<StreamContext>::Get(
       resource_context, kStreamContextKeyName);
 }
 
 HostZoomMap* GetHostZoomMapForResourceContext(ResourceContext* context) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  return static_cast<NonOwningZoomData*>(
-      context->GetUserData(kHostZoomMapKeyName))->host_zoom_map();
+  NonOwningZoomData* result = static_cast<NonOwningZoomData*>(
+      context->GetUserData(kHostZoomMapKeyName));
+  if (!result)
+    return NULL;
+  return result->host_zoom_map();
 }
 
 URLDataManagerBackend* GetURLDataManagerForResourceContext(
     ResourceContext* context) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
   if (!context->GetUserData(kURLDataManagerBackendKeyName)) {
     context->SetUserData(kURLDataManagerBackendKeyName,
                          new URLDataManagerBackend());
   }
   return static_cast<URLDataManagerBackend*>(
@@ skipping 18 matching lines @@
   // store a non-owning pointer here.
   resource_context->SetUserData(
       kHostZoomMapKeyName,
       new NonOwningZoomData(
           HostZoomMap::GetForBrowserContext(browser_context)));
 
   resource_context->DetachUserDataThread();
 }
 
 }  // namespace content