Call addFile() before getErrors() to actually get errors.

pkg/analyzer_cli/lib/src/analyzer_impl.dart

Index: pkg/analyzer_cli/lib/src/analyzer_impl.dart
diff --git a/pkg/analyzer_cli/lib/src/analyzer_impl.dart b/pkg/analyzer_cli/lib/src/analyzer_impl.dart
index 256b70d9a8a57ace935f72fcc9dc357ea54e532f..c8ce07edc06fd4fa8cec3e49f1e5396c7a5ca38d 100644
--- a/pkg/analyzer_cli/lib/src/analyzer_impl.dart
+++ b/pkg/analyzer_cli/lib/src/analyzer_impl.dart
@@ -132,6 +132,7 @@ class AnalyzerImpl {
       for (Source source in sources) {
         if (analysisDriver != null) {
           String path = source.fullName;
+          analysisDriver.addFile(path);
           ErrorsResult errorsResult = await analysisDriver.getErrors(path);
           errorInfos.add(new AnalysisErrorInfoImpl(
               errorsResult.errors, errorsResult.lineInfo));