Fix newly introduced errors and warnings

pkg/analyzer/test/src/task/dart_work_manager_test.dart

 // Copyright (c) 2015, 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 analyzer.test.src.task.dart_work_manager_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/error/error.dart' show AnalysisError;
 import 'package:analyzer/exception/exception.dart';
 import 'package:analyzer/src/context/cache.dart';
@@ skipping 339 matching lines @@
   void test_getLibrariesContainingPart_askResultProvider() {
     Source part1 = new TestSource('part1.dart');
     Source part2 = new TestSource('part2.dart');
     Source part3 = new TestSource('part3.dart');
     Source library1 = new TestSource('library1.dart');
     Source library2 = new TestSource('library2.dart');
     // configure AnalysisContext mock
     when(context.aboutToComputeResult(anyObject, CONTAINING_LIBRARIES))
         .thenInvoke((CacheEntry entry, ResultDescriptor result) {
       if (entry.target == part1) {
-        entry.setValue(result, <Source>[library1, library2], []);
+        entry.setValue(result as ResultDescriptor<List<Source>>,
+            <Source>[library1, library2], []);
         return true;
       }
       if (entry.target == part2) {
-        entry.setValue(result, <Source>[library2], []);
+        entry.setValue(
+            result as ResultDescriptor<List<Source>>, <Source>[library2], []);
         return true;
       }
       return false;
     });
     // getLibrariesContainingPart
     expect(manager.getLibrariesContainingPart(part1),
         unorderedEquals([library1, library2]));
     expect(
         manager.getLibrariesContainingPart(part2), unorderedEquals([library2]));
     expect(manager.getLibrariesContainingPart(part3), isEmpty);
@@ skipping 481 matching lines @@
 class _SourceFactoryMock extends TypedMock implements SourceFactory {}
 
 class _SourceMock extends TypedMock implements Source {
   final String shortName;
   _SourceMock(this.shortName);
   @override
   String get fullName => '/' + shortName;
   @override
   String toString() => fullName;
 }