Get more tests passing using the new task model

pkg/analyzer/lib/src/task/dart.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.src.task.dart;
 
 import 'dart:collection';
 import 'dart:math' as math;
 
 import 'package:analyzer/src/context/cache.dart';
@@ skipping 3363 matching lines @@
    */
   ScanDartTask(InternalAnalysisContext context, AnalysisTarget target)
       : super(context, target);
 
   @override
   TaskDescriptor get descriptor => DESCRIPTOR;
 
   @override
   void internalPerform() {
     Source source = getRequiredSource();
+
+    RecordingErrorListener errorListener = new RecordingErrorListener();
+    if (context.getModificationStamp(target.source) < 0) {
+      String message = 'Content could not be read';
+      if (context is InternalAnalysisContext) {
+        CacheEntry entry = (context as InternalAnalysisContext).getCacheEntry(target);
+        CaughtException exception = entry.exception;
+        if (exception != null) {
+          message = exception.toString();
+        }
+      }
+      errorListener.onError(new AnalysisError(
+          source, 0, 0, ScannerErrorCode.UNABLE_GET_CONTENT, [message]));
+    }
     if (target is DartScript) {
       DartScript script = target;
       List<ScriptFragment> fragments = script.fragments;
       if (fragments.length < 1) {
         throw new AnalysisException('Cannot scan scripts with no fragments');
       } else if (fragments.length > 1) {
         throw new AnalysisException(
             'Cannot scan scripts with multiple fragments');
       }
       ScriptFragment fragment = fragments[0];
 
-      RecordingErrorListener errorListener = new RecordingErrorListener();
       Scanner scanner = new Scanner(source,
           new SubSequenceReader(fragment.content, fragment.offset),
           errorListener);
       scanner.setSourceStart(fragment.line, fragment.column);
       scanner.preserveComments = context.analysisOptions.preserveComments;
       scanner.enableNullAwareOperators =
           context.analysisOptions.enableNullAwareOperators;
 
       outputs[TOKEN_STREAM] = scanner.tokenize();
       outputs[LINE_INFO] = new LineInfo(scanner.lineStarts);
       outputs[SCAN_ERRORS] = removeDuplicateErrors(errorListener.errors);
     } else if (target is Source) {
       String content = getRequiredInput(CONTENT_INPUT_NAME);
 
-      RecordingErrorListener errorListener = new RecordingErrorListener();
       Scanner scanner =
           new Scanner(source, new CharSequenceReader(content), errorListener);
       scanner.preserveComments = context.analysisOptions.preserveComments;
       scanner.enableNullAwareOperators =
           context.analysisOptions.enableNullAwareOperators;
 
       outputs[TOKEN_STREAM] = scanner.tokenize();
       outputs[LINE_INFO] = new LineInfo(scanner.lineStarts);
       outputs[SCAN_ERRORS] = removeDuplicateErrors(errorListener.errors);
     } else {
@@ skipping 254 matching lines @@
 
   @override
   bool moveNext() {
     if (_newSources.isEmpty) {
       return false;
     }
     currentTarget = _newSources.removeLast();
     return true;
   }
 }