Return MaybeHandle from NewRaw???String.

src/handles.h

Index: src/handles.h
diff --git a/src/handles.h b/src/handles.h
index 77e5e528da6e2fa04ea7386fe6ff00bd79394401..5b5ed1b564bd57e2648edfb35d74f2832026ecd8 100644
--- a/src/handles.h
+++ b/src/handles.h
@@ -72,7 +72,8 @@ class MaybeHandle {
     return Handle<T>(location_);
   }
 
-  INLINE(bool ToHandle(Handle<T>* out)) {
+  // Convert to a Handle with a type that can be upcasted to.
+  template <class S> INLINE(bool ToHandle(Handle<S>* out)) {
     if (location_ == NULL) {
       *out = Handle<T>::null();
       return false;
@@ -82,6 +83,8 @@ class MaybeHandle {
     }
   }
 
+  bool is_null() const { return location_ == NULL; }
+
  protected:
   T** location_;