Refactorings for TranslateUri and its tests.

pkg/front_end/lib/src/fasta/target_implementation.dart

 // Copyright (c) 2016, 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 fasta.target_implementation;
 
 import 'package:kernel/target/targets.dart' as backend show Target;
 
 import 'builder/builder.dart' show Builder, ClassBuilder, LibraryBuilder;
 
@@ skipping 83 matching lines @@
     for (String uri in backendTarget.extraRequiredLibraries) {
       loader.read(Uri.parse(uri), -1);
     }
   }
 
   void addSourceInformation(
       Uri uri, List<int> lineStarts, List<int> sourceCode);
 
   void readPatchFiles(LibraryBuilder library) {
     assert(library.uri.scheme == "dart");
-    List<Uri> patches = uriTranslator.patches[library.uri.path];
+    List<Uri> patches = uriTranslator.dartPatches[library.uri.path];
     if (patches != null) {
       for (Uri patch in patches) {
         library.loader.read(patch, -1, fileUri: patch, isPatch: true);
       }
     }
   }
 }