Add the --steal-breakpoints flag.

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index 6f8c417f16198b2e65f069ab529475e816065422..dbf4b51a979901eb3da21a512ad089d5d31dcb2f 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -669,6 +669,9 @@ class Isolate : public BaseIsolate {
 
   Counters* counters() { return &counters_; }
 
+  // Handle service messages until we are told to resume execution.
+  void PauseEventHandler();
+
  private:
   Isolate();
   explicit Isolate(Isolate* original);
@@ -774,6 +777,9 @@ class Isolate : public BaseIsolate {
   // Isolate list next pointer.
   Isolate* next_;
 
+  // Used to wake the isolate when it is in the pause event loop.
+  Monitor* pause_loop_monitor_;
+
   // Reusable handles support.
 #define REUSABLE_HANDLE_FIELDS(object)                                         \
   object* object##_handle_;
@@ -805,6 +811,8 @@ class Isolate : public BaseIsolate {
   static Dart_EntropySource entropy_source_callback_;
   static Dart_IsolateInterruptCallback vmstats_callback_;
 
+  static void WakePauseEventHandler(Dart_Isolate isolate);
+
   // Manage list of existing isolates.
   static void AddIsolateTolist(Isolate* isolate);
   static void RemoveIsolateFromList(Isolate* isolate);