Improvements to task model

pkg/analyzer/lib/task/general.dart

Index: pkg/analyzer/lib/task/general.dart
diff --git a/pkg/analyzer/lib/task/general.dart b/pkg/analyzer/lib/task/general.dart
index 76e50b971f585e555aa5ce74e20d4b4734ac5466..791e8e7db14a05d8c3da7a89f80d71faf8d1a456 100644
--- a/pkg/analyzer/lib/task/general.dart
+++ b/pkg/analyzer/lib/task/general.dart
@@ -20,28 +20,30 @@ import 'package:analyzer/task/model.dart';
 // 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);