refactor/cleanup dart completion cache

pkg/analysis_server/test/services/completion/imported_computer_test.dart

 // Copyright (c) 2014, 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 test.services.completion.toplevel;
 
 import 'package:analysis_server/src/protocol.dart';
 import 'package:analysis_server/src/services/completion/completion_manager.dart';
 import 'package:analysis_server/src/services/completion/dart_completion_cache.dart';
 import 'package:analysis_server/src/services/completion/dart_completion_manager.dart';
 import 'package:analysis_server/src/services/completion/imported_computer.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../reflective_tests.dart';
 import 'completion_test_util.dart';
+import 'package:analyzer/src/generated/element.dart';
 
 main() {
   groupSep = ' | ';
   runReflectiveTests(ImportedComputerTest);
 }
 
 @ReflectiveTestCase()
 class ImportedComputerTest extends AbstractSelectorSuggestionTest {
 
   void assertCached(String completion) {
@@ skipping 79 matching lines @@
 
   @override
   void setUpComputer() {
     computer = new ImportedComputer(shouldWaitForLowPrioritySuggestions: true);
   }
 
   @override
   test_ArgumentList() {
     return super.test_ArgumentList().then((_) {
       expect(request.cache.importKey, "import '/libA.dart';");
+      ClassElement objClassElem1 = request.cache.importedClassMap['Object'];
+      expect(objClassElem1, isNotNull);
+      ClassElement objClassElem2 = request.cache.objectClassElement;
+      expect(objClassElem1, same(objClassElem2));
     });
   }
 
   @override
   test_ArgumentList_imported_function() {
     return super.test_ArgumentList_imported_function().then((_) {
       expect(request.cache.importKey, "import '/libA.dart';");
     });
   }
 
@@ skipping 77 matching lines @@
     (computer as ImportedComputer).shouldWaitForLowPrioritySuggestions = false;
     computeFast();
     return computeFull((bool result) {
       assertSuggestImportedClass('C');
       // Assert computer does not wait for or include low priority results
       // from non-imported libraries unless instructed to do so.
       assertNotSuggested('H');
     });
   }
 }