fs_event: use cached Persistent syms instead

Instead of String::New every time, use a Persistent sym. This can be
accomplished in two ways:

1) Local<String> str = *persistent_str_sym;

2) Handle<String> str = persistent_str_sym;

I've chosen to use the latter method for simplicity's sake.

Other small changes include creating syms on Initialize and removing
unnecessary Local casting on return values.

src/fs_event_wrap.cc

@@ -28,7 +28,9 @@ using namespace v8;
 
 namespace node {
 
+static Persistent<String> change_sym;
 static Persistent<String> onchange_sym;
+static Persistent<String> rename_sym;
 
 class FSEventWrap: public HandleWrap {
 public:
@@ -76,6 +78,10 @@ void FSEventWrap::Initialize(Handle<Object> target) {
   target->Set(String::NewSymbol("FSEvent"),
               Persistent<FunctionTemplate>::New(node_isolate,
                                                 t)->GetFunction());
+
+  change_sym = NODE_PSYMBOL("change");
+  onchange_sym = NODE_PSYMBOL("onchange");
+  rename_sym = NODE_PSYMBOL("rename");
 }
 
 
@@ -118,7 +124,7 @@ Handle<Value> FSEventWrap::Start(const Arguments& args) {
 void FSEventWrap::OnEvent(uv_fs_event_t* handle, const char* filename,
     int events, int status) {
   HandleScope scope(node_isolate);
-  Local<String> eventStr;
+  Handle<String> eventStr;
 
   FSEventWrap* wrap = static_cast<FSEventWrap*>(handle->data);
 
@@ -140,27 +146,22 @@ void FSEventWrap::OnEvent(uv_fs_event_t* handle, const char* filename,
     eventStr = String::Empty(node_isolate);
   }
   else if (events & UV_RENAME) {
-    eventStr = String::New("rename");
+    eventStr = rename_sym;
   }
   else if (events & UV_CHANGE) {
-    eventStr = String::New("change");
+    eventStr = change_sym;
   }
   else {
     assert(0 && "bad fs events flag");
     abort();
   }
 
-  Local<Value> argv[3] = {
+  Handle<Value> argv[3] = {
     Integer::New(status, node_isolate),
     eventStr,
-    filename ? static_cast<Local<Value> >(String::New(filename))
+    filename ? String::New(filename) : v8::Null(node_isolate)
-             : Local<Value>::New(node_isolate, v8::Null(node_isolate))
   };
 
-  if (onchange_sym.IsEmpty()) {
-    onchange_sym = NODE_PSYMBOL("onchange");
-  }
-
   MakeCallback(wrap->object_, onchange_sym, ARRAY_SIZE(argv), argv);
 }