Make debugger step into bound callbacks passed to Array.forEach.

src/collection.js

Index: src/collection.js
diff --git a/src/collection.js b/src/collection.js
index c8cf639f97d96c3396f463a97ad5181ac4ccc347..9868bded6b0bf2940145eb29c5d9a47f3222b4e4 100644
--- a/src/collection.js
+++ b/src/collection.js
@@ -105,7 +105,7 @@ function SetForEach(f, receiver) {
 
   var iterator = new SetIterator(this, ITERATOR_KIND_VALUES);
   var key;
-  var stepping = DEBUG_IS_ACTIVE && %DebugCallbackSupportsStepping(f);
+  var stepping = DEBUG_IS_STEPPING();
   var value_array = [UNDEFINED];
   while (%SetIteratorNext(iterator, value_array)) {
     if (stepping) %DebugPrepareStepInIfStepping(f);
@@ -247,7 +247,7 @@ function MapForEach(f, receiver) {
   }
 
   var iterator = new MapIterator(this, ITERATOR_KIND_ENTRIES);
-  var stepping = DEBUG_IS_ACTIVE && %DebugCallbackSupportsStepping(f);
+  var stepping = DEBUG_IS_STEPPING();
   var value_array = [UNDEFINED, UNDEFINED];
   while (%MapIteratorNext(iterator, value_array)) {
     if (stepping) %DebugPrepareStepInIfStepping(f);