Add ImportElement and ExportElement

tests/compiler/dart2js/reexport_handled_test.dart

 // Copyright (c) 2013, 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 reexport_handled_test;
 
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
 import 'mock_compiler.dart';
 import 'package:compiler/src/elements/elements.dart'
@@ skipping 14 matching lines @@
 
 void main() {
   MockCompiler compiler;
   asyncTest(() => MockCompiler.create((MockCompiler c) {
     compiler = c;
     compiler.registerSource(exportingLibraryUri, EXPORTING_LIBRARY_SOURCE);
     compiler.registerSource(reexportingLibraryUri, REEXPORTING_LIBRARY_SOURCE);
     return compiler.libraryLoader.loadLibrary(exportingLibraryUri);
   }).then((exportingLibrary) {
     Expect.isTrue(exportingLibrary.exportsHandled);
-    var foo = findInExports(exportingLibrary, 'foo');
+    var foo = exportingLibrary.findExported('foo');
     Expect.isNotNull(foo);
     Expect.isTrue(foo.isField);
 
     // Load reexporting library when exports are handled on the exporting library.
     return compiler.libraryLoader.loadLibrary(reexportingLibraryUri);
   }).then((reexportingLibrary) {
-    var foo = findInExports(reexportingLibrary, 'foo');
+    var foo = reexportingLibrary.findExported('foo');
     Expect.isNotNull(foo);
     Expect.isTrue(foo.isField);
   }));
 }
-
-Element findInExports(LibraryElement library, String name) {
-  for (var export in library.exports) {
-    if (export.name == name) {
-      return export;
-    }
-  }
-  return null;
-}