Update V8 to r6768 as required by WebKit r78450

Change-Id: Ib8868ff7147a76547a8d1d85f257ebe8546a3d3f
diff --git a/src/factory.h b/src/factory.h
index a5e1591..7547f7c 100644
--- a/src/factory.h
+++ b/src/factory.h
@@ -196,6 +196,8 @@
 
   static Handle<Map> GetSlowElementsMap(Handle<Map> map);
 
+  static Handle<Map> GetPixelArrayElementsMap(Handle<Map> map);
+
   static Handle<FixedArray> CopyFixedArray(Handle<FixedArray> array);
 
   // Numbers (eg, literals) are pretenured by the parser.
@@ -365,6 +367,15 @@
       Handle<SerializedScopeInfo> scope_info);
   static Handle<SharedFunctionInfo> NewSharedFunctionInfo(Handle<String> name);
 
+  static Handle<JSMessageObject> NewJSMessageObject(
+      Handle<String> type,
+      Handle<JSArray> arguments,
+      int start_position,
+      int end_position,
+      Handle<Object> script,
+      Handle<Object> stack_trace,
+      Handle<Object> stack_frames);
+
   static Handle<NumberDictionary> DictionaryAtNumberPut(
       Handle<NumberDictionary>,
       uint32_t key,