Allow stepping into Object.observe handlers.

src/runtime/runtime-debug.cc

 // Copyright 2014 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.
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
 #include "src/arguments.h"
 #include "src/debug.h"
 #include "src/deoptimizer.h"
@@ skipping 2714 matching lines @@
 
   if (found.is_null()) return heap->undefined_value();
   return *Script::GetWrapper(found);
 }
 
 
 // Check whether debugger and is about to step into the callback that is passed
 // to a built-in function such as Array.forEach.
 RUNTIME_FUNCTION(Runtime_DebugCallbackSupportsStepping) {
   DCHECK(args.length() == 1);
-  if (!isolate->debug()->is_active() || !isolate->debug()->StepInActive()) {
+  Debug* debug = isolate->debug();
+  if (!debug->is_active() || !debug->IsStepping() ||
+      debug->last_step_action() != StepIn) {
     return isolate->heap()->false_value();
   }
   CONVERT_ARG_CHECKED(Object, callback, 0);
   // We do not step into the callback if it's a builtin or not even a function.
   return isolate->heap()->ToBoolean(callback->IsJSFunction() &&
                                     !JSFunction::cast(callback)->IsBuiltin());
 }
 
 
 // Set one shot breakpoints for the callback function that is passed to a
@@ skipping 62 matching lines @@
   return Smi::FromInt(isolate->debug()->is_active());
 }
 
 
 RUNTIME_FUNCTION(RuntimeReference_DebugBreakInOptimizedCode) {
   UNIMPLEMENTED();
   return NULL;
 }
 }
 }  // namespace v8::internal