Fix a bug where breakpoints where not getting properly deleted.

runtime/vm/debugger.h

Index: runtime/vm/debugger.h
diff --git a/runtime/vm/debugger.h b/runtime/vm/debugger.h
index acb69ec747c3b2dc2072674e173d94de14d6de5c..5696e963a39b72aa3cca33a11317d2a6e287ce30 100644
--- a/runtime/vm/debugger.h
+++ b/runtime/vm/debugger.h
@@ -651,7 +651,8 @@ class Debugger {
   // interrupts, etc.
   void Pause(DebuggerEvent* event);
 
-  void HandleSteppingRequest(DebuggerStackTrace* stack_trace);
+  void HandleSteppingRequest(DebuggerStackTrace* stack_trace,
+                             bool skip_next_step = false);
 
   Isolate* isolate_;
   Dart_Port isolate_id_;  // A unique ID for the isolate in the debugger.
@@ -690,6 +691,11 @@ class Debugger {
   // lower on the stack.
   uword stepping_fp_;
 
+  // If we step while at a breakpoint, we would hit the same pc twice.
+  // We use this field to let us skip the next single-step after a
+  // breakpoint.
+  bool skip_next_step_;
+
   Dart_ExceptionPauseInfo exc_pause_info_;
 
   static EventHandler* event_handler_;