API functions returning Promises should not throw exceptions.

Source/bindings/v8/V8Binding.h

 /*
 * Copyright (C) 2009 Google Inc. All rights reserved.
 * Copyright (C) 2012 Ericsson AB. 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.
@@ skipping 431 matching lines @@
 // FIXME: Remove the special casing for NodeFilter and XPathNSResolver.
 PassRefPtr<NodeFilter> toNodeFilter(v8::Handle<v8::Value>, v8::Isolate*);
 PassRefPtrWillBeRawPtr<XPathNSResolver> toXPathNSResolver(v8::Handle<v8::Value>, v8::Isolate*);
 
 template<class T> struct NativeValueTraits;
 
 template<>
 struct NativeValueTraits<String> {
     static inline String nativeValue(const v8::Handle<v8::Value>& value, v8::Isolate* isolate)
     {
-        TOSTRING_BOOL(V8StringResource<>, stringValue, value, String());
+        V8StringResource<> stringValue = value;
+        if (UNLIKELY(!stringValue.prepare())) {
+            return String();
+        }
         return stringValue;
     }
 };
 
 template<>
 struct NativeValueTraits<unsigned> {
     static inline unsigned nativeValue(const v8::Handle<v8::Value>& value, v8::Isolate* isolate)
     {
         return toUInt32(value);
     }
@@ skipping 296 matching lines @@
 
 private:
     v8::HandleScope m_handleScope;
     v8::Context::Scope m_contextScope;
     RefPtr<NewScriptState> m_scriptState;
 };
 
 } // namespace WebCore
 
 #endif // V8Binding_h