Always return computed errors, even for not added files.

pkg/analyzer/lib/src/dart/analysis/driver.dart

Index: pkg/analyzer/lib/src/dart/analysis/driver.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/driver.dart b/pkg/analyzer/lib/src/dart/analysis/driver.dart
index 043d415bf30e07ed1b8d242393b0896ccc650a47..18b7fb1bafa390d038557fa0cd3f19ab7317098b 100644
--- a/pkg/analyzer/lib/src/dart/analysis/driver.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/driver.dart
@@ -786,7 +786,6 @@ class AnalysisDriver {
           AnalysisResult result = _getAnalysisResultFromBytes(
               file, signature, bytes,
               content: withUnit ? file.content : null,
-              withErrors: _fileTracker.addedFiles.contains(path),
               resolvedUnit: withUnit ? resolvedUnit : null);
           if (withUnit && _priorityFiles.contains(path)) {
             _priorityResults[path] = result;
@@ -877,11 +876,9 @@ class AnalysisDriver {
    */
   AnalysisResult _getAnalysisResultFromBytes(
       FileState file, String signature, List<int> bytes,
-      {String content, bool withErrors: true, CompilationUnit resolvedUnit}) {
+      {String content, CompilationUnit resolvedUnit}) {
     var unit = new AnalysisDriverResolvedUnit.fromBuffer(bytes);
-    List<AnalysisError> errors = withErrors
-        ? _getErrorsFromSerialized(file, unit.errors)
-        : const <AnalysisError>[];
+    List<AnalysisError> errors = _getErrorsFromSerialized(file, unit.errors);
     return new AnalysisResult(
         this,
         _sourceFactory,