Reland "Prepare blink to unify definitions of load completion"

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 4d3ff96a1ac053636e8a697d2ffd131227bb2919..07f425e96736ecb0eb1deae65edf166f7b45226e 100644
--- a/Source/core/dom/Document.h
+++ b/Source/core/dom/Document.h
@@ -906,6 +906,7 @@ public:
     bool loadEventFinished() const { return m_loadEventProgress >= LoadEventCompleted; }
     bool unloadStarted() const { return m_loadEventProgress >= PageHideInProgress; }
     bool processingBeforeUnload() const { return m_loadEventProgress == BeforeUnloadEventInProgress; }
+    void suppressLoadEvent() { m_loadEventProgress = LoadEventCompleted; }
 
     void setContainsPlugins() { m_containsPlugins = true; }
     bool containsPlugins() const { return m_containsPlugins; }