bindings: Add empty checks for toV8()

Source/bindings/core/v8/ScriptPromiseProperty.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ScriptPromiseProperty_h
 #define ScriptPromiseProperty_h
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptPromisePropertyBase.h"
 #include "bindings/core/v8/ToV8.h"
@@ skipping 102 matching lines @@
     if (!executionContext() || executionContext()->activeDOMObjectsAreStopped())
         return;
     m_rejected = value;
     resolveOrReject(Rejected);
 }
 
 template<typename HolderType, typename ResolvedType, typename RejectedType>
 v8::Handle<v8::Object> ScriptPromiseProperty<HolderType, ResolvedType, RejectedType>::holder(v8::Handle<v8::Object> creationContext, v8::Isolate* isolate)
 {
     v8::Handle<v8::Value> value = toV8(m_holder, creationContext, isolate);
+    if (value.IsEmpty())
+        return v8::Handle<v8::Object>();
     return value.As<v8::Object>();
 }
 
 template<typename HolderType, typename ResolvedType, typename RejectedType>
 v8::Handle<v8::Value> ScriptPromiseProperty<HolderType, ResolvedType, RejectedType>::resolvedValue(v8::Isolate* isolate, v8::Handle<v8::Object> creationContext)
 {
     ASSERT(state() == Resolved);
     return toV8(m_resolved, creationContext, isolate);
 }
 
@@ skipping 23 matching lines @@
 {
     TraceIfNeeded<HolderType>::trace(visitor, &m_holder);
     TraceIfNeeded<ResolvedType>::trace(visitor, &m_resolved);
     TraceIfNeeded<RejectedType>::trace(visitor, &m_rejected);
     ScriptPromisePropertyBase::trace(visitor);
 }
 
 } // namespace blink
 
 #endif // ScriptPromiseProperty_h