Implement File.directory() and File.directorySync() to get

runtime/bin/file_impl.dart

Index: runtime/bin/file_impl.dart
diff --git a/runtime/bin/file_impl.dart b/runtime/bin/file_impl.dart
index 9efffbef622c31c7858117ade266a9a487471d4a..a4966bd7954dd936a4d720d6b29be38f4b22990c 100644
--- a/runtime/bin/file_impl.dart
+++ b/runtime/bin/file_impl.dart
@@ -404,6 +404,24 @@ class _DeleteOperation extends _FileOperation {
 }
 
 
+class _DirectoryOperation extends _FileOperation {
+  _DirectoryOperation(String this._name);
+
+  void execute(ReceivePort port) {
+    if (_name is String) {
+      if (_FileUtils.exists(_name)) {
+        _replyPort.send(_FileUtils.directory(_name), port.toSendPort());
+        return;
+      }
+    }
+    // Either _name is not a string or the file does not exist.
+    _replyPort.send(null, port.toSendPort());
+  }
+
+  String _name;
+}
+
+
 class _ExitOperation extends _FileOperation {
   void execute(ReceivePort port) {
     port.close();
@@ -479,6 +497,7 @@ class _FileUtils {
   static int open(String name, int mode) native "File_Open";
   static bool create(String name) native "File_Create";
   static bool delete(String name) native "File_Delete";
+  static bool directory(String name) native "File_Directory";
   static String fullPath(String name) native "File_FullPath";
   static int close(int id) native "File_Close";
   static int readByte(int id) native "File_ReadByte";
@@ -637,6 +656,32 @@ class _File implements File {
     }
   }
 
+  void directory() {
+    _asyncUsed = true;
+    var handleDirectoryResult = (path, ignored) {
+      var handler =
+          (_directoryHandler != null) ? _directoryHandler : (s) => null;
+      if (path != null) {
+        handler(new Directory(path));
+      } else if (_errorHandler != null) {
+        _errorHandler("Cannot get containing directory for: ${_name}");
+      }
+    };
+    var operation = new _DirectoryOperation(_name);
+    _scheduler.enqueue(operation, handleDirectoryResult);
+  }
+
+  void directorySync() {
+    if (_asyncUsed) {
+      throw new FileIOException(
+          "Mixed use of synchronous and asynchronous API");
+    }
+    if (!existsSync()) {
+      throw new FileIOException("Cannot get directory for: $_name");
+    }
+    return new Directory(_FileUtils.directory(_name));
+  }
+
   void open([FileMode mode = FileMode.READ]) {
     _asyncUsed = true;
     if (mode != FileMode.READ &&
@@ -796,6 +841,10 @@ class _File implements File {
     _deleteHandler = handler;
   }
 
+  void set directoryHandler(void handler(String path)) {
+    _directoryHandler = handler;
+  }
+
   void set openHandler(void handler(RandomAccessFile file)) {
     _openHandler = handler;
   }
@@ -824,6 +873,7 @@ class _File implements File {
   Function _existsHandler;
   Function _createHandler;
   Function _deleteHandler;
+  Function _directoryHandler;
   Function _openHandler;
   Function _inputStreamHandler;
   Function _outputStreamHandler;