Add support for resolving symbolic links

pkg/analyzer/lib/file_system/memory_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.memory_file_system;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
 import 'dart:core' hide Resource;
@@ skipping 12 matching lines @@
 class MemoryResourceProvider implements ResourceProvider {
   final Map<String, _MemoryResource> _pathToResource =
       new HashMap<String, _MemoryResource>();
   final Map<String, List<int>> _pathToBytes = new HashMap<String, List<int>>();
   final Map<String, int> _pathToTimestamp = new HashMap<String, int>();
   final Map<String, List<StreamController<WatchEvent>>> _pathToWatchers =
       new HashMap<String, List<StreamController<WatchEvent>>>();
   int nextStamp = 0;
 
   final Context _pathContext;
+
   @override
   final AbsolutePathContext absolutePathContext;
 
   MemoryResourceProvider({bool isWindows: false})
       : _pathContext = isWindows ? windows : posix,
         absolutePathContext = new AbsolutePathContext(isWindows);
 
   @override
   Context get pathContext => _pathContext;
 
@@ skipping 259 matching lines @@
   String readAsStringSync() {
     throw new FileSystemException(path, 'File could not be read');
   }
 
   @override
   File renameSync(String newPath) {
     throw new FileSystemException(path, 'File could not be renamed');
   }
 
   @override
+  File resolveSymbolicLinksSync() {
+    return throw new FileSystemException(path, "File does not exist");
+  }
+
+  @override
   Uri toUri() => new Uri.file(path, windows: _provider.pathContext == windows);
 
   @override
   void writeAsBytesSync(List<int> bytes) {
     throw new FileSystemException(path, 'File could not be written');
   }
 
   @override
   void writeAsStringSync(String content) {
     throw new FileSystemException(path, 'File could not be written');
@@ skipping 52 matching lines @@
     }
     return UTF8.decode(content);
   }
 
   @override
   File renameSync(String newPath) {
     return _provider.renameFileSync(this, newPath);
   }
 
   @override
+  File resolveSymbolicLinksSync() => this;
+
+  @override
   Uri toUri() => new Uri.file(path, windows: _provider.pathContext == windows);
 
   @override
   void writeAsBytesSync(List<int> bytes) {
     _provider._setFileContent(this, bytes);
   }
 
   @override
   void writeAsStringSync(String content) {
     _provider._setFileContent(this, UTF8.encode(content));
@@ skipping 130 matching lines @@
   bool operator ==(other) {
     if (runtimeType != other.runtimeType) {
       return false;
     }
     return path == other.path;
   }
 
   @override
   String toString() => path;
 }