Update V8 to r5017 as required by WebKit r62496

Change-Id: I1b4b7718d1d77ceef07f543e9150a2cb3a628f3a
diff --git a/src/handles.h b/src/handles.h
index 96b17a6..1e14daf 100644
--- a/src/handles.h
+++ b/src/handles.h
@@ -193,8 +193,14 @@
 void NormalizeElements(Handle<JSObject> object);
 void TransformToFastProperties(Handle<JSObject> object,
                                int unused_property_fields);
+
+// Flattens a string.
 void FlattenString(Handle<String> str);
 
+// Flattens a string and returns the underlying external or sequential
+// string.
+Handle<String> FlattenGetString(Handle<String> str);
+
 Handle<Object> SetProperty(Handle<JSObject> object,
                            Handle<String> key,
                            Handle<Object> value,