Fix updating packages map on reload and add a regression test

runtime/observatory/lib/src/service/object.dart

Index: runtime/observatory/lib/src/service/object.dart
diff --git a/runtime/observatory/lib/src/service/object.dart b/runtime/observatory/lib/src/service/object.dart
index 3f99b907bb3361b5a81a3f98ef6eca9ce56d3419..0e941b9f633e0119a89157a42addcdec0152ac86 100644
--- a/runtime/observatory/lib/src/service/object.dart
+++ b/runtime/observatory/lib/src/service/object.dart
@@ -1356,11 +1356,15 @@ class Isolate extends ServiceObjectOwner implements M.Isolate {
     return invokeRpc('getSourceReport', params);
   }
 
-  Future<ServiceMap> reloadSources({String rootLibUri, bool pause}) {
+  Future<ServiceMap> reloadSources(
+      {String rootLibUri, String packagesUri, bool pause}) {
     Map<String, dynamic> params = <String, dynamic>{};
     if (rootLibUri != null) {
       params['rootLibUri'] = rootLibUri;
     }
+    if (packagesUri != null) {
+      params['packagesUri'] = packagesUri;
+    }
     if (pause != null) {
       params['pause'] = pause;
     }