Only propagate reload errors when there are Dart frames on the stack.

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

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of service;
 
 // Some value smaller than the object ring, so requesting a large array
 // doesn't result in an expired ref because the elements lapped it in the
 // object ring.
 const int kDefaultFieldLimit = 100;
@@ skipping 1348 matching lines @@
     if (pause != null) {
       params['pause'] = pause;
     }
     return invokeRpc('reloadSources', params).then((result) {
       _cache.clear();
       return result;
     });
   }
 
   void _handleIsolateReloadEvent(ServiceEvent event) {
-    if (event.reloadError != null) {
-      // Failure.
-      print('Reload failed: ${event.reloadError}');
-    } else {
+    if (event.reloadError == null) {
       _cache.clear();
     }
   }
 
   /// Fetches and builds the class hierarchy for this isolate. Returns the
   /// Object class object.
   Future<Class> getClassHierarchy() {
     return invokeRpc('getClassList', {})
         .then(_loadClasses)
         .then(_buildClassHierarchy);
@@ skipping 723 matching lines @@
   }
 
   String kind;
   DateTime timestamp;
   List<M.Breakpoint> pauseBreakpoints;
   Breakpoint breakpoint;
   Frame topFrame;
   DartError error;
   String extensionRPC;
   Instance exception;
-  Instance reloadError;
+  DartError reloadError;
   bool atAsyncSuspension;
   Instance inspectee;
   ByteData data;
   int count;
   String reason;
   String exceptions;
   String bytesAsString;
   Map logRecord;
   String extensionKind;
   Map extensionData;
@@ skipping 2440 matching lines @@
     var v = list[i];
     if ((v is Map) && _isServiceMap(v)) {
       list[i] = owner.getFromMap(v);
     } else if (v is List) {
       _upgradeList(v, owner);
     } else if (v is Map) {
       _upgradeMap(v, owner);
     }
   }
 }