DartWorkManager.getLibrariesContainingPart() should ask the ResultProvider for CONTAINING_LIBRARIES.

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/src/context/cache.dart';
 import 'package:analyzer/src/dart/scanner/scanner.dart' show ScannerErrorCode;
 import 'package:analyzer/src/generated/engine.dart'
@@ skipping 311 matching lines @@
         new AnalysisError(source1, 1, 0, ScannerErrorCode.MISSING_DIGIT);
     AnalysisError error2 =
         new AnalysisError(source1, 2, 0, ScannerErrorCode.MISSING_DIGIT);
     when(context.getLibrariesContaining(source1)).thenReturn([source2]);
     entry1.setValue(DART_ERRORS, <AnalysisError>[error1, error2], []);
     List<AnalysisError> errors = manager.getErrors(source1);
     expect(errors, unorderedEquals([error1, error2]));
   }
 
   void test_getLibrariesContainingPart() {
+    when(context.aboutToComputeResult(anyObject, anyObject)).thenReturn(false);
     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');
     manager.partLibrariesMap[part1] = [library1, library2];
     manager.partLibrariesMap[part2] = [library2];
     manager.libraryPartsMap[library1] = [part1];
     manager.libraryPartsMap[library2] = [part1, part2];
     // getLibrariesContainingPart
@@ skipping 479 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;
 }