allow computeErrors to work on non-.dart files

pkg/analyzer/lib/src/context/context.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.context.context;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/instrumentation/instrumentation.dart';
@@ skipping 565 matching lines @@
       return null;
     }
     String code = getContents(source).data;
     String comment = code.substring(docRange.offset, docRange.end);
     return comment.replaceAll('\r\n', '\n');
   }
 
   @override
   List<AnalysisError> computeErrors(Source source) {
     String name = source.shortName;
-    if (AnalysisEngine.isDartFileName(name)) {
-      return computeResult(source, DART_ERRORS);
-    } else if (AnalysisEngine.isHtmlFileName(name)) {
+    if (AnalysisEngine.isHtmlFileName(name)) {
       return computeResult(source, HTML_ERRORS);
     }
-    return AnalysisError.NO_ERRORS;
+    return computeResult(source, DART_ERRORS);
   }
 
   @override
   List<Source> computeExportedLibraries(Source source) =>
       computeResult(source, EXPORTED_LIBRARIES);
 
   @override
   @deprecated
   HtmlElement computeHtmlElement(Source source) {
     // TODO(brianwilkerson) Remove this method after switching to the new task
@@ skipping 1486 matching lines @@
         new PendingFuture<T>(_context, target, computeValue);
     if (!pendingFuture.evaluate(entry)) {
       _context._pendingFutureTargets
           .putIfAbsent(target, () => <PendingFuture>[])
           .add(pendingFuture);
       scheduleComputation();
     }
     return pendingFuture.future;
   }
 }