Don't schedule LIBRARY_ERRORS_READY for libraries that should not be analyzed.

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 test.src.task.dart_work_manager_test;
 
 import 'package:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/engine.dart'
     show
@@ skipping 488 matching lines @@
     manager.resultsComputed(
         new LibrarySpecificUnit(source1, source2), {RESOLVED_UNIT: unit});
     ChangeNoticeImpl notice = context.getNotice(source2);
     expect(notice.parsedDartUnit, isNull);
     expect(notice.resolvedDartUnit, unit);
     expect(notice.lineInfo, lineInfo);
   }
 
   void test_resultsComputed_sourceKind_isLibrary() {
     manager.unknownSourceQueue.addAll([source1, source2, source3]);
+    when(context.shouldErrorsBeAnalyzed(source2, null)).thenReturn(true);
     manager.resultsComputed(source2, {SOURCE_KIND: SourceKind.LIBRARY});
     expect_librarySourceQueue([source2]);
     expect_unknownSourceQueue([source1, source3]);
   }
 
   void test_resultsComputed_sourceKind_isPart() {
     manager.unknownSourceQueue.addAll([source1, source2, source3]);
     manager.resultsComputed(source2, {SOURCE_KIND: SourceKind.PART});
     expect_librarySourceQueue([]);
     expect_unknownSourceQueue([source1, source3]);
@@ skipping 22 matching lines @@
   }
 
   @override
   ChangeNoticeImpl getNotice(Source source) {
     return _pendingNotices.putIfAbsent(
         source, () => new ChangeNoticeImpl(source));
   }
 
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 }