Further reduce use of Element in codegen.

tests/compiler/dart2js/patch_test.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.
 
 import 'dart:async';
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/diagnostics/messages.dart' show MessageKind;
 import 'package:compiler/src/elements/elements.dart';
@@ skipping 976 matching lines @@
   ensure(compiler, "clear", cls.lookupLocalMember,
       checkHasBody: true, expectIsPatched: true);
 
   compiler.phase = Compiler.PHASE_DONE_RESOLVING;
 
   // Check that a method just in the patch class is a target for a
   // typed selector.
   Selector selector =
       new Selector.call(const PublicName('method'), CallStructure.NO_ARGS);
   TypeMask typeMask = new TypeMask.exact(cls, world);
-  FunctionElement method = cls.implementation.lookupLocalMember('method');
+  MethodElement method = cls.implementation.lookupLocalMember('method');
   method.computeType(compiler.resolution);
   Expect.isTrue(selector.applies(method));
   Expect.isTrue(typeMask.canHit(method, selector, world));
 
   // Check that the declaration method in the declaration class is a target
   // for a typed selector.
   selector =
       new Selector.call(const PublicName('clear'), CallStructure.NO_ARGS);
   typeMask = new TypeMask.exact(cls, world);
   method = cls.lookupLocalMember('clear');
@@ skipping 165 matching lines @@
     await testPatchNonFunction();
 
     await testPatchAndSelector();
 
     await testEffectiveTarget();
 
     await testAnalyzeAllInjectedMembers();
     await testTypecheckPatchedMembers();
   });
 }