Status page indicator for contexts w/o .packages.

For diagnostic purposes.

See: https://github.com/dart-lang/sdk/issues/24900 for more context.

BUG=24900
R=scheglov@google.com

Review URL: https://codereview.chromium.org/1436343002 .
diff --git a/pkg/analysis_server/lib/src/status/get_handler.dart b/pkg/analysis_server/lib/src/status/get_handler.dart
index 66ee196..a83d95e 100644
--- a/pkg/analysis_server/lib/src/status/get_handler.dart
+++ b/pkg/analysis_server/lib/src/status/get_handler.dart
@@ -1345,6 +1345,9 @@
         String key = folder.shortName;
         buffer.write(makeLink(CONTEXT_PATH, {CONTEXT_QUERY_PARAM: folder.path},
             key, _hasException(folderMap[folder])));
+        if (!folder.getChild('.packages').exists) {
+          buffer.write(' <b>[No .packages file]</b>');
+        }
       });
       // TODO(brianwilkerson) Add items for the SDK contexts (currently only one).
       buffer.write('</p>');