Make DocumentLoader::timing return a reference

Source/modules/performance/SharedWorkerPerformance.cpp

Index: Source/modules/performance/SharedWorkerPerformance.cpp
diff --git a/Source/modules/performance/SharedWorkerPerformance.cpp b/Source/modules/performance/SharedWorkerPerformance.cpp
index 074c2ce8b32a5c1d92747df4abe1421b01243ac2..90fbea53f6488a89961e53bfe9900044d0e3ad86 100644
--- a/Source/modules/performance/SharedWorkerPerformance.cpp
+++ b/Source/modules/performance/SharedWorkerPerformance.cpp
@@ -71,7 +71,7 @@ double SharedWorkerPerformance::getWorkerStart(ExecutionContext* context, Shared
     if (!document->loader())
         return 0;
 
-    double navigationStart = document->loader()->timing()->navigationStart();
+    double navigationStart = document->loader()->timing().navigationStart();
     return m_timeOrigin - navigationStart;
 }