Do not fire didStartLoading and didStopLoading events twice.

Source/core/dom/Document.h

Index: Source/core/dom/Document.h
diff --git a/Source/core/dom/Document.h b/Source/core/dom/Document.h
index ff8de6407bb41b0f7bc41229f1799f4e54f9e066..4c162eaab4def1948774fa053393f48dac487904 100644
--- a/Source/core/dom/Document.h
+++ b/Source/core/dom/Document.h
@@ -911,6 +911,7 @@ public:
     bool loadEventFinished() const { return m_loadEventProgress >= LoadEventCompleted; }
     bool unloadStarted() const { return m_loadEventProgress >= PageHideInProgress; }
     bool processingBeforeUnload() const { return m_loadEventProgress == BeforeUnloadEventInProgress; }
+    bool isLoadEventCompleted() const { return m_loadEventProgress == LoadEventCompleted; }
     void suppressLoadEvent();
 
     void setContainsPlugins() { m_containsPlugins = true; }