Have Frame::tree() return a reference

Source/core/inspector/InspectorApplicationCacheAgent.cpp

Index: Source/core/inspector/InspectorApplicationCacheAgent.cpp
diff --git a/Source/core/inspector/InspectorApplicationCacheAgent.cpp b/Source/core/inspector/InspectorApplicationCacheAgent.cpp
index 968b913f3ec9bb390495bf18472352283292f9dd..be045acb3241419b873c88e12552840dd10b2df1 100644
--- a/Source/core/inspector/InspectorApplicationCacheAgent.cpp
+++ b/Source/core/inspector/InspectorApplicationCacheAgent.cpp
@@ -102,7 +102,7 @@ void InspectorApplicationCacheAgent::getFramesWithManifests(ErrorString*, RefPtr
     result = TypeBuilder::Array<TypeBuilder::ApplicationCache::FrameWithManifest>::create();
 
     Frame* mainFrame = m_pageAgent->mainFrame();
-    for (Frame* frame = mainFrame; frame; frame = frame->tree()->traverseNext(mainFrame)) {
+    for (Frame* frame = mainFrame; frame; frame = frame->tree().traverseNext(mainFrame)) {
         DocumentLoader* documentLoader = frame->loader()->documentLoader();
         if (!documentLoader)
             continue;