[es6] Implement spec compliant ToPrimitive in the runtime.

src/debug/debug.cc

Index: src/debug/debug.cc
diff --git a/src/debug/debug.cc b/src/debug/debug.cc
index 99036d71e7e7c6df559e192591ff1d36598e35ef..de7cc2315d02397e85f54388772acf6f4da68b67 100644
--- a/src/debug/debug.cc
+++ b/src/debug/debug.cc
@@ -2148,7 +2148,7 @@ void Debug::NotifyMessageHandler(v8::DebugEvent event,
       Handle<Object> exception;
       if (!maybe_exception.ToHandle(&exception)) break;
       Handle<Object> result;
-      if (!Execution::ToString(isolate_, exception).ToHandle(&result)) break;
+      if (!Object::ToString(isolate_, exception).ToHandle(&result)) break;
       answer = Handle<String>::cast(result);
     }