Use a pool of native ports for directory operations

runtime/bin/directory_impl.dart

Index: runtime/bin/directory_impl.dart
diff --git a/runtime/bin/directory_impl.dart b/runtime/bin/directory_impl.dart
index f3efa6aeb3a56b5f0bd10dc4048152a8ee1df6d1..e1e46ebcbe2975f7650695753fa5797ac55f65a0 100644
--- a/runtime/bin/directory_impl.dart
+++ b/runtime/bin/directory_impl.dart
@@ -27,9 +27,7 @@ class _Directory implements Directory {
   static SendPort _newServicePort() native "Directory_NewServicePort";
 
   void exists(void callback(bool exists)) {
-    if (_directoryService == null) {
-      _directoryService = _newServicePort();
-    }
+    _ensureDirectoryService();
     List request = new List(2);
     request[0] = kExistsRequest;
     request[1] = _path;
@@ -53,9 +51,7 @@ class _Directory implements Directory {
   }
 
   void create(void callback()) {
-    if (_directoryService == null) {
-      _directoryService = _newServicePort();
-    }
+    _ensureDirectoryService();
     List request = new List(2);
     request[0] = kCreateRequest;
     request[1] = _path;
@@ -75,9 +71,7 @@ class _Directory implements Directory {
   }
 
   void createTemp(void callback()) {
-    if (_directoryService == null) {
-      _directoryService = _newServicePort();
-    }
+    _ensureDirectoryService();
     List request = new List(2);
     request[0] = kCreateTempRequest;
     request[1] = _path;
@@ -106,9 +100,7 @@ class _Directory implements Directory {
   }
 
   void _deleteHelper(bool recursive, String errorMsg, void callback()) {
-    if (_directoryService == null) {
-      _directoryService = _newServicePort();
-    }
+    _ensureDirectoryService();
     List request = new List(3);
     request[0] = kDeleteRequest;
     request[1] = _path;
@@ -199,14 +191,14 @@ class _Directory implements Directory {
     _onError = onError;
   }
 
-  void _closePort(ReceivePort port) {
-    if (port !== null) {
-      port.close();
+  String get path() { return _path; }
+
+  void _ensureDirectoryService() {
+    if (_directoryService == null) {
+      _directoryService = _newServicePort();
     }
   }
 
-  String get path() { return _path; }
-
   var _onDir;
   var _onFile;
   var _onDone;