ScriptPromise should check the constructor paraemter.

Source/bindings/v8/ScriptPromise.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 34 matching lines @@
 // ScriptPromise is the class for representing Promise values in C++ world.
 // ScriptPromise holds a Promise.
 // So holding a ScriptPromise as a member variable in DOM object causes
 // memory leaks since it has a reference from C++ to V8.
 //
 class ScriptPromise {
 public:
     // Constructs an empty promise.
     ScriptPromise() { }
 
-    // Constructs a ScriptPromise from |value|.
-    // i.e. the constructed ScriptPromise holds |Promise.cast(value)|.
-    // Note: if |value| is a non-Promise value, two ScriptPromises constructed
-    // with it hold different Promises each other.
-    explicit ScriptPromise(const ScriptValue& /* value */);
-
-    ScriptPromise(v8::Handle<v8::Value> promise, v8::Isolate* isolate)
-        : m_promise(promise, isolate)
-    {
-        ASSERT(!m_promise.hasNoValue());
-    }
+    // Constructs a ScriptPromise from |promise|.
+    // If |promise| is not a Promise object, throws a v8 TypeError.
+    ScriptPromise(v8::Handle<v8::Value> promise, v8::Isolate*);
 
     ScriptPromise then(PassOwnPtr<ScriptFunction> onFulfilled, PassOwnPtr<ScriptFunction> onRejected = PassOwnPtr<ScriptFunction>());
 
     bool isObject() const
     {
         return m_promise.isObject();
     }
 
     bool isNull() const
     {
@@ skipping 20 matching lines @@
         return m_promise.hasNoValue();
     }
 
     void clear()
     {
         m_promise.clear();
     }
 
     static ScriptPromise createPending();
     static ScriptPromise createPending(ExecutionContext*);
+    // Constructs and returns a ScriptPromise from |value|.
+    // if |value| is not a Promise object, returns a Promise object
+    // resolved with |value|.
+    static ScriptPromise cast(const ScriptValue& /*value*/);
 
 private:
     ScriptValue m_promise;
 };
 
 } // namespace WebCore
 
 
 #endif // ScriptPromise_h