Server notification to indicate `pub list-dir` fallback.

pkg/analysis_server/lib/src/context_manager.dart

Index: pkg/analysis_server/lib/src/context_manager.dart
diff --git a/pkg/analysis_server/lib/src/context_manager.dart b/pkg/analysis_server/lib/src/context_manager.dart
index d429e22a4c82d1d30c9dfbd99741d5ed5af02317..e135e9a4ae23b87e3127e0140dc79c8a1ba78a6a 100644
--- a/pkg/analysis_server/lib/src/context_manager.dart
+++ b/pkg/analysis_server/lib/src/context_manager.dart
@@ -838,6 +838,12 @@ class ContextManagerImpl implements ContextManager {
             return new CustomPackageResolverDisposition(resolver);
           }
         }
+
+        // Notify server that no `.packages` file was found (and there is no
+        // alternative resolver provider).
+        AnalysisEngine.instance.logger.logError(
+            'No `.packages` for $folder, falling back to `pub`.');
+
         ServerPerformanceStatistics.pub.makeCurrentWhile(() {
           packageMapInfo = _packageMapProvider.computePackageMap(folder);
         });