Add the --steal-breakpoints flag.

runtime/vm/debugger.cc

Index: runtime/vm/debugger.cc
diff --git a/runtime/vm/debugger.cc b/runtime/vm/debugger.cc
index b1783fa85f19d5776f9cf16c57b1f038dd6bc9b7..8c741eadec8d89ea8b423574f0a21c5bb81770ed 100644
--- a/runtime/vm/debugger.cc
+++ b/runtime/vm/debugger.cc
@@ -35,6 +35,9 @@ DEFINE_FLAG(bool, show_invisible_frames, false,
 DEFINE_FLAG(bool, trace_debugger_stacktrace, false,
             "Trace debugger stacktrace collection");
 DEFINE_FLAG(bool, verbose_debug, false, "Verbose debugger messages");
+DEFINE_FLAG(bool, steal_breakpoints, false,
+            "Intercept breakpoints and other pause events before they "

[rmacnak, 2015/04/30 21:48:55]

Should probably indicate they go to the vm service/observatory instead.

[turnidge, 2015/05/01 16:54:15]

Done.

+            "are sent to the embedder");
 
 
 Debugger::EventHandler* Debugger::event_handler_ = NULL;
@@ -239,7 +242,10 @@ void Debugger::InvokeEventHandler(DebuggerEvent* event) {
     Service::HandleEvent(&service_event);
   }
 
-  if (event_handler_ != NULL) {
+  if (FLAG_steal_breakpoints && event->IsPauseEvent()) {
+    // We allow the embedder's default breakpoint handler to be overridden.
+    isolate_->PauseEventHandler();
+  } else if (event_handler_ != NULL) {
     (*event_handler_)(event);
   }