Refactor prototype setting code and expose SetPrototype to public V8 API.

src/handles.cc

Index: src/handles.cc
diff --git a/src/handles.cc b/src/handles.cc
index 909d6e6a2213dc37a846835eafb61da31ee78a9d..936177dbba393ce28de4d6f11a90b1f57b75973b 100644
--- a/src/handles.cc
+++ b/src/handles.cc
@@ -300,6 +300,12 @@ Handle<Object> GetPrototype(Handle<Object> obj) {
 }
 
 
+Handle<Object> SetPrototype(Handle<JSObject> obj, Handle<Object> value) {
+  const bool skip_hidden_prototypes = false;
+  CALL_HEAP_FUNCTION(obj->SetPrototype(*value, skip_hidden_prototypes), Object);
+}
+
+
 Handle<Object> GetHiddenProperties(Handle<JSObject> obj,
                                    bool create_if_needed) {
   Object* holder = obj->BypassGlobalProxy();