Implement rewind: drop one or more frames from the debugger.

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 c638dd90d9f4a0bf88b162f28d10e2337f86bc70..ade0146205e53003407ba1a5c8e6b7d556b5682c 100644
--- a/runtime/observatory/lib/src/service/object.dart
+++ b/runtime/observatory/lib/src/service/object.dart
@@ -42,11 +42,13 @@ class ServerRpcException extends RpcException implements M.RequestException {
   static const kStreamNotSubscribed = 104;
   static const kIsolateMustBeRunnable = 105;
   static const kIsolateMustBePaused = 106;
+  static const kCannotResume = 107;
   static const kIsolateIsReloading = 1000;
   static const kFileSystemAlreadyExists = 1001;
   static const kFileSystemDoesNotExist = 1002;
   static const kFileDoesNotExist = 1003;
   static const kIsolateReloadFailed = 1004;
+  static const kIsolateReloadBarred = 1005;
 
   int code;
   Map data;
@@ -1344,6 +1346,7 @@ class Isolate extends ServiceObjectOwner implements M.Isolate {
       params['pause'] = pause;
     }
     return invokeRpc('reloadSources', params).then((result) {
+      _cache.clear();
       reloading = true;

[Cutch, 2016/11/22 22:27:50]

why are we tracking this reloading bit?

[turnidge, 2016/11/22 22:54:06]

Perhaps we were going to use it to track isolate status back when reloading was
asynchronous.  But it doesn't seem to be used for anything right now.  Removing.

       return result;
     });
@@ -1768,6 +1771,10 @@ class Isolate extends ServiceObjectOwner implements M.Isolate {
     return invokeRpc('resume', {'step': 'Out'});
   }
 
+  Future rewind(int count) {
+    return invokeRpc('resume', {'step': 'Rewind', 'frameIndex': count});
+  }
+
   Future setName(String newName) {
     return invokeRpc('setName', {'name': newName});
   }