Improvements to task model

pkg/analyzer/lib/task/general.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.task.general;
 
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/task/model.dart';
 
 /**
  * The analysis errors associated with a target.
  *
  * The value combines errors represented by multiple other results.
  */
 // TODO(brianwilkerson) If we want to associate errors with targets smaller than
 // a file, we will need other contribution points to collect them. In which case
 // we might want to rename this and/or document that it applies to files. For
 // that matter, we might also want to have one that applies to Dart files and a
 // different one that applies to HTML files, because the list of errors being
 // combined is likely to be different.
 final ContributionPoint<List<AnalysisError>> ANALYSIS_ERRORS =
-    new ContributionPoint<List<AnalysisError>>('ANALYSIS_ERRORS');
+    new ContributionPoint<List<AnalysisError>>(
+        'ANALYSIS_ERRORS',
+        AnalysisError.NO_ERRORS);
 
 /**
  * The contents of a single file.
  */
 final ResultDescriptor<String> CONTENT =
-    new ResultDescriptor<String>('CONTENT');
+    new ResultDescriptor<String>('CONTENT', null);
 
 /**
  * The line information for a single file.
  */
 final ResultDescriptor<LineInfo> LINE_INFO =
-    new ResultDescriptor<LineInfo>('LINE_INFO');
+    new ResultDescriptor<LineInfo>('LINE_INFO', null);
 
 /**
  * The modification time of a file.
  */
 final ResultDescriptor<int> MODIFICATION_TIME =
-    new ResultDescriptor<int>('MODIFICATION_TIME');
+    new ResultDescriptor<int>('MODIFICATION_TIME', -1);
 
 /**
  * The kind of a [Source].
  */
 final ResultDescriptor<SourceKind> SOURCE_KIND =
-    new ResultDescriptor<SourceKind>('SOURCE_KIND');
+    new ResultDescriptor<SourceKind>('SOURCE_KIND', SourceKind.UNKNOWN);