Fix assumption: HttpTransactionFactory::GetCache() may return NULL.

content/browser/web_contents/web_contents_impl.cc

Index: content/browser/web_contents/web_contents_impl.cc
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index 5d51ed15e1126ee4cc38385cde2171e82d2739d3..d47a6ef362c8157626ee30e86106e2604b0cfb80 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -152,8 +152,10 @@ void NotifyCacheOnIO(
     scoped_refptr<net::URLRequestContextGetter> request_context,
     const GURL& url,
     const std::string& http_method) {
-  request_context->GetURLRequestContext()->http_transaction_factory()->
-      GetCache()->OnExternalCacheHit(url, http_method);
+  net::HttpCache* cache = request_context->GetURLRequestContext()->
+      http_transaction_factory()->GetCache();
+  if (cache)
+    cache->OnExternalCacheHit(url, http_method);
 }
 
 // Helper function for retrieving all the sites in a frame tree.