Revert "Revert "First step towards having patch files for generic libraries.""

tests/compiler/dart2js/mock_compiler.dart

 // Copyright (c) 2012, 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('mock_compiler');
 
 #import("dart:uri");
 
 #import("../../../lib/compiler/implementation/elements/elements.dart");
 #import("../../../lib/compiler/implementation/leg.dart");
@@ skipping 138 matching lines @@
   }
 
   void scanBuiltinLibraries() {
     // Do nothing. The mock core library is already handled in the constructor.
   }
 
   LibraryElement scanBuiltinLibrary(String name) {
     // Do nothing. The mock core library is already handled in the constructor.
   }
 
+  // The mock library doesn't need any patches.
+  Uri resolvePatchUri(String dartLibraryName) => null;
+
   Script readScript(Uri uri, [ScriptTag node]) {
     String code = sources[uri.toString()];
     if (code === null) throw new IllegalArgumentException(uri);
     return new StringScript(code);
   }
 }
 
 void compareWarningKinds(String text, expectedWarnings, foundWarnings) {
   var fail = (message) => Expect.fail('$text: $message');
   Iterator<MessageKind> expected = expectedWarnings.iterator();
@@ skipping 31 matching lines @@
   importLibrary(library, compiler.coreLibrary, compiler);
   return library;
 }
 
 class StringScript extends Script {
   final String code;
   StringScript(this.code) : super(null, null);
   String get text() => code;
   String get name() => "mock script";
 }