Handle stepping requests after isolate interrupt event

runtime/vm/debugger.h

Index: runtime/vm/debugger.h
===================================================================
--- runtime/vm/debugger.h	(revision 32907)
+++ runtime/vm/debugger.h	(working copy)
@@ -367,7 +367,8 @@
   void DebuggerStepCallback();
 
   void SignalExceptionThrown(const Instance& exc);
-  static void SignalIsolateEvent(EventType type);
+  void SignalIsolateEvent(EventType type);
+  static void SignalIsolateInterrupted();
 
   uword GetPatchedStubAddress(uword breakpoint_address);
 
@@ -442,6 +443,8 @@
   // interrupts, etc.
   void Pause(DebuggerEvent* event);
 
+  void HandleSteppingRequest(DebuggerStackTrace* stack_trace);
+
   Isolate* isolate_;
   Dart_Port isolate_id_;  // A unique ID for the isolate in the debugger.
   bool initialized_;