Remove unneeded HandleScopes.

It's not necessary to create HandleScope in v8 native binding functions,
because it's guarrenteed that the there is a upper HandleScope when the
native function is called. So unless we are urgent to free the handles,
not using HandleScope in native binding functions is a cleaner and safer
choice.

common/api/atom_api_screen.cc

@@ -67,8 +67,6 @@ void Screen::GetPrimaryDisplay(
 
 // static
 void Screen::Initialize(v8::Handle<v8::Object> target) {
-  v8::HandleScope handle_scope(node_isolate);
-
   v8::Local<v8::FunctionTemplate> t = v8::FunctionTemplate::New(New);
   t->InstanceTemplate()->SetInternalFieldCount(1);
   t->SetClassName(v8::String::NewSymbol("Screen"));