Allow stepping into Object.observe handlers.

src/debug.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_DEBUG_H_
 #define V8_DEBUG_H_
 
 #include "src/allocation.h"
 #include "src/arguments.h"
 #include "src/assembler.h"
@@ skipping 392 matching lines @@
                    StackFrame::Id frame_id);
   void ClearStepping();
   void ClearStepOut();
   bool IsStepping() { return thread_local_.step_count_ > 0; }
   bool StepNextContinue(BreakLocationIterator* break_location_iterator,
                         JavaScriptFrame* frame);
   bool StepInActive() { return thread_local_.step_into_fp_ != 0; }
   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();
 
   // Returns whether the operation succeeded. Compilation can only be triggered
   // if a valid closure is passed as the second argument, otherwise the shared
   // function needs to be compiled already.
   bool EnsureDebugInfo(Handle<SharedFunctionInfo> shared,
                        Handle<JSFunction> function);
   static Handle<DebugInfo> GetDebugInfo(Handle<SharedFunctionInfo> shared);
@@ skipping 327 matching lines @@
   // several frames above.
   // There is no calling conventions here, because it never actually gets
   // called, it only gets returned to.
   static void GenerateFrameDropperLiveEdit(MacroAssembler* masm);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_DEBUG_H_