Add ResolutionResult as intermediate value in ResolutionVisitor and use it to mark assert.

tests/compiler/dart2js/resolver_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 "package:expect/expect.dart";
 import 'dart:async';
 import "package:async_helper/async_helper.dart";
 import 'dart:collection';
 
 import "package:compiler/implementation/resolution/resolution.dart";
@@ skipping 21 matching lines @@
       locals.add(buildIdentifier(name));
     }
   }
   var definitions = new NodeList(null, LinkFromList(locals), null, null);
   return new VariableDefinitions(null, Modifiers.EMPTY, definitions);
 }
 
 Future testLocals(List variables) {
   return MockCompiler.create((MockCompiler compiler) {
     ResolverVisitor visitor = compiler.resolverVisitor();
-    Element element = visitor.visit(createLocals(variables));
+    ResolutionResult result = visitor.visit(createLocals(variables));
+    Element element = result != null ? result.element : null;
     // A VariableDefinitions does not have an element.
     Expect.equals(null, element);
     Expect.equals(variables.length, map(visitor).length);
 
     for (final variable in variables) {
       final name = variable[0];
       Identifier id = buildIdentifier(name);
-      final VariableElement variableElement = visitor.visit(id);
+      ResolutionResult result = visitor.visit(id);
+      final VariableElement variableElement =
+          result != null ? result.element : null;
       MethodScope scope = visitor.scope;
       Expect.equals(variableElement, scope.elements[name]);
     }
     return compiler;
   });
 }
 
 main() {
   asyncTest(() => Future.forEach([
     testLocalsOne,
@@ skipping 1020 matching lines @@
       }""";
   asyncTest(() => compileScript(script2).then((compiler) {
     expect(compiler,
         [MessageKind.CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS],
         [MessageKind.CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS_CONSTRUCTOR,
          MessageKind.CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS_CONSTRUCTOR,
          MessageKind.CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS_FIELD,
          MessageKind.CONST_CONSTRUCTOR_WITH_NONFINAL_FIELDS_FIELD]);
   }));
 }