Reland "Prepare blink to unify definitions of load completion"

Source/core/fetch/Resource.h

Index: Source/core/fetch/Resource.h
diff --git a/Source/core/fetch/Resource.h b/Source/core/fetch/Resource.h
index 1342a92de8313a479883a5b4c99ad080a5c304cc..af0525d91bd8b6d030efbe7f5c54430728246eac 100644
--- a/Source/core/fetch/Resource.h
+++ b/Source/core/fetch/Resource.h
@@ -175,7 +175,8 @@ public:
 
     // Computes the status of an object after loading.
     // Updates the expire date on the cache entry file
-    void finish(double finishTime = 0.0);
+    void setLoadFinishTime(double finishTime) { m_loadFinishTime = finishTime; }
+    void finish();
 
     // FIXME: Remove the stringless variant once all the callsites' error messages are updated.
     bool passesAccessControlCheck(SecurityOrigin*);