Add Folder.getChildAssumingFile().

pkg/analyzer/lib/file_system/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.file_system;
 
 import 'dart:async';
 
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/util/absolute_path.dart';
@@ skipping 88 matching lines @@
    */
   bool contains(String path);
 
   /**
    * Return an existing child [Resource] with the given [relPath].
    * Return a not existing [File] if no such child exist.
    */
   Resource getChild(String relPath);
 
   /**
+   * Return a [File] representing a child [Resource] with the given
+   * [relPath].  This call does not check whether a file with the given name
+   * exists on the filesystem - client must call the [File]'s `exists` getter
+   * to determine whether the folder actually exists.
+   */
+  File getChildAssumingFile(String relPath);
+
+  /**
    * Return a [Folder] representing a child [Resource] with the given
    * [relPath].  This call does not check whether a folder with the given name
    * exists on the filesystem--client must call the [Folder]'s `exists` getter
    * to determine whether the folder actually exists.
    */
   Folder getChildAssumingFolder(String relPath);
 
   /**
    * Return a list of existing direct children [Resource]s (folders and files)
    * in this folder, in no particular order.
@@ skipping 106 matching lines @@
 
   @override
   Uri restoreAbsolute(Source source) =>
       _provider.pathContext.toUri(source.fullName);
 
   /**
    * Return `true` if the given [uri] is a `file` URI.
    */
   static bool _isFileUri(Uri uri) => uri.scheme == _FILE_SCHEME;
 }