Request construction spec changes to use the 'used' flag.

Source/modules/serviceworkers/Body.h

Index: Source/modules/serviceworkers/Body.h
diff --git a/Source/modules/serviceworkers/Body.h b/Source/modules/serviceworkers/Body.h
index 99072c95adf9ae6f24953bfd9bc6b91dfb492bb4..06e14eac636d2d9cfe5d6333c46b4f038d6bc550 100644
--- a/Source/modules/serviceworkers/Body.h
+++ b/Source/modules/serviceworkers/Body.h
@@ -50,6 +50,11 @@ public:
 
     virtual void trace(Visitor*) { }
 
+protected:
+    // Sets the bodyUsed flag to true. This signifies that the contents of the
+    // body have been consumed and cannot be accessed again.
+    void setBodyUsed();
+
 private:
     ScriptPromise readAsync(ScriptState*, ResponseType);
     void resolveJSON();