Add support for resolving symbolic links

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 analyzer.file_system.physical_file_system;
 
 import 'dart:async';
 import 'dart:core' hide Resource;
 import 'dart:io' as io;
 
@@ skipping 111 matching lines @@
  */
 class _PhysicalFile extends _PhysicalResource implements File {
   _PhysicalFile(io.File file) : super(file);
 
   @override
   Stream<WatchEvent> get changes => new FileWatcher(_entry.path).events;
 
   @override
   int get modificationStamp {
     try {
-      io.File file = _entry as io.File;
-      return file.lastModifiedSync().millisecondsSinceEpoch;
+      return _file.lastModifiedSync().millisecondsSinceEpoch;
     } on io.FileSystemException catch (exception) {
       throw new FileSystemException(exception.path, exception.message);
     }
   }
 
+  /**
+   * Return the underlying file being represented by this wrapper.
+   */
+  io.File get _file => _entry as io.File;
+
   @override
   Source createSource([Uri uri]) {
     return new FileSource(this, uri ?? pathContext.toUri(path));
   }
 
   @override
   bool isOrContains(String path) {
     return path == this.path;
   }
 
   @override
   List<int> readAsBytesSync() {
     try {
-      io.File file = _entry as io.File;
-      return file.readAsBytesSync();
+      return _file.readAsBytesSync();
     } on io.FileSystemException catch (exception) {
       throw new FileSystemException(exception.path, exception.message);
     }
   }
 
   @override
   String readAsStringSync() {
     try {
-      io.File file = _entry as io.File;
-      return FileBasedSource.fileReadMode(file.readAsStringSync());
+      return FileBasedSource.fileReadMode(_file.readAsStringSync());
     } on io.FileSystemException catch (exception) {
       throw new FileSystemException(exception.path, exception.message);
     }
   }
 
   @override
   File renameSync(String newPath) {
     try {
-      io.File file = _entry as io.File;
-      io.File newFile = file.renameSync(newPath);
-      return new _PhysicalFile(newFile);
+      return new _PhysicalFile(_file.renameSync(newPath));
     } on io.FileSystemException catch (exception) {
       throw new FileSystemException(exception.path, exception.message);
     }
+  }
+
+  @override
+  File resolveSymbolicLinksSync() {
+    try {
+      return new _PhysicalFile(new io.File(_file.resolveSymbolicLinksSync()));
+    } on io.FileSystemException catch (exception) {
+      throw new FileSystemException(exception.path, exception.message);
+    }
   }
 
   @override
   Uri toUri() => new Uri.file(path);
 
   @override
   void writeAsBytesSync(List<int> bytes) {
     try {
-      io.File file = _entry as io.File;
-      file.writeAsBytesSync(bytes);
+      _file.writeAsBytesSync(bytes);
     } on io.FileSystemException catch (exception) {
       throw new FileSystemException(exception.path, exception.message);
     }
   }
 
   @override
   void writeAsStringSync(String content) {
     try {
-      io.File file = _entry as io.File;
-      file.writeAsStringSync(content);
+      _file.writeAsStringSync(content);
     } 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 {
@@ skipping 145 matching lines @@
           timer.cancel();
         }
       });
       return completer.future;
     }
     _isSpawning = true;
     _runner = await IsolateRunner.spawn();
     return _runner;
   }
 }