Fix possible crash when HostZoomMap is NULL

content/browser/resource_context_impl.cc

Index: content/browser/resource_context_impl.cc
diff --git a/content/browser/resource_context_impl.cc b/content/browser/resource_context_impl.cc
index 14115a4887c77b6d081bba0fec8eb789a9480da0..6cd05277a87a96d0b46b13f034cbc75f999e03d9 100644
--- a/content/browser/resource_context_impl.cc
+++ b/content/browser/resource_context_impl.cc
@@ -94,8 +94,11 @@ StreamContext* GetStreamContextForResourceContext(
 
 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(