API functions returning Promises should not throw exceptions.

Source/bindings/v8/V8Binding.h

Index: Source/bindings/v8/V8Binding.h
diff --git a/Source/bindings/v8/V8Binding.h b/Source/bindings/v8/V8Binding.h
index f7349bd84d866209371698d9c3b5aa27d26c791e..9df3459b72321a5246616c4f480e916c9c124d9b 100644
--- a/Source/bindings/v8/V8Binding.h
+++ b/Source/bindings/v8/V8Binding.h
@@ -449,7 +449,10 @@ 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;
     }
 };