allow computeErrors to work on non-.dart files

pkg/analyzer/lib/src/context/context.dart

Index: pkg/analyzer/lib/src/context/context.dart
diff --git a/pkg/analyzer/lib/src/context/context.dart b/pkg/analyzer/lib/src/context/context.dart
index 893ae9f5a51642d64268b47f3040c7614057614a..8674f94f7a9ebb6d71afc3ff7f726edd028c0be2 100644
--- a/pkg/analyzer/lib/src/context/context.dart
+++ b/pkg/analyzer/lib/src/context/context.dart
@@ -583,12 +583,10 @@ class AnalysisContextImpl implements InternalAnalysisContext {
   @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