Revert "Package map source factory support" [TBR].

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:core' hide Resource;
 import 'dart:io' as io;
 
@@ skipping 23 matching lines @@
   PhysicalResourceProvider(String fileReadMode(String s)) {
     if (fileReadMode != null) {
       FileBasedSource.fileReadMode = fileReadMode;
     }
   }
 
   @override
   Context get pathContext => io.Platform.isWindows ? windows : posix;
 
   @override
-  File getFile(String path) => new _PhysicalFile(new io.File(path));
-
-  @override
-  Folder getFolder(String path) => new _PhysicalFolder(new io.Directory(path));
-
-  @override
   Resource getResource(String path) {
     if (io.FileSystemEntity.isDirectorySync(path)) {
-      return getFolder(path);
+      io.Directory directory = new io.Directory(path);
+      return new _PhysicalFolder(directory);
     } else {
-      return getFile(path);
+      io.File file = new io.File(path);
+      return new _PhysicalFile(file);
     }
   }
 
   @override
   Folder getStateLocation(String pluginId) {
     String home;
     if (io.Platform.isWindows) {
       home = io.Platform.environment['LOCALAPPDATA'];
     } else {
       home = io.Platform.environment['HOME'];
@@ skipping 148 matching lines @@
   bool operator ==(other) {
     if (runtimeType != other.runtimeType) {
       return false;
     }
     return path == other.path;
   }
 
   @override
   String toString() => path;
 }