Add readAsStringSync() to File.

pkg/analyzer/lib/file_system/physical_file_system.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library physical_file_system;
 
 import 'dart:async';
 import 'dart:io' as io;
 
 import 'package:analyzer/src/generated/java_io.dart';
@@ skipping 80 matching lines @@
     if (uri == null) {
       uri = javaFile.toURI();
     }
     return new FileBasedSource.con2(uri, javaFile);
   }
 
   @override
   bool isOrContains(String path) {
     return path == this.path;
   }
+
+  @override
+  String readAsStringSync() {
+    try {
+      io.File file = _entry as io.File;
+      return file.readAsStringSync();
+    } on io.FileSystemException catch (exception) {
+      throw new FileSystemException(exception.path, exception.message);
+    }
+  }
 }
 
 /**
  * A `dart:io` based implementation of [Folder].
  */
 class _PhysicalFolder extends _PhysicalResource implements Folder {
   _PhysicalFolder(io.Directory directory) : super(directory);
 
   @override
   Stream<WatchEvent> get changes => new DirectoryWatcher(_entry.path).events;
@@ skipping 84 matching lines @@
   bool operator ==(other) {
     if (runtimeType != other.runtimeType) {
       return false;
     }
     return path == other.path;
   }
 
   @override
   String toString() => path;
 }