Allow stepping into Object.observe handlers.

src/debug.h

Index: src/debug.h
diff --git a/src/debug.h b/src/debug.h
index b8348fd52af0dbd4656e4ea88ec3535d1656591b..15590a983631016326ebd8247c0e68f52158ba27 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -410,6 +410,7 @@ class Debug {
   void HandleStepIn(Handle<Object> function_obj, Handle<Object> holder,
                     Address fp, bool is_constructor);
   bool StepOutActive() { return thread_local_.step_out_fp_ != 0; }
+  StepAction LastStepAction() { return thread_local_.last_step_action_; }

[Yang, 2014/11/18 11:46:39]

I'm curious why StepInActive is no longer sufficient. Did anything break?

[aandrey, 2014/11/18 11:52:24]

A StepIn action may not necessarily lead to StepInActive() being true. e.g. a
StepIn may actually result in calling ActivateStepOut() instead.

In this patch we "promote" StepIn to also step into microtasks (and/or across
js->c++->js boundaries).
Otherwise, there is no way to step into Promise/O.o callbacks other than setting
a breakpoint.

 
   // Purge all code objects that have no debug break slots.
   void PrepareForBreakPoints();