[debugger] flood function for stepping before calling it.

src/js/collection.js

Index: src/js/collection.js
diff --git a/src/js/collection.js b/src/js/collection.js
index 6d75f4a5bd7646607fa4e6dd6b5317715c699f4c..221f0e107831a486599ccb00f7e18dc4e728364b 100644
--- a/src/js/collection.js
+++ b/src/js/collection.js
@@ -248,10 +248,8 @@ function SetForEach(f, receiver) {
 
   var iterator = new SetIterator(this, ITERATOR_KIND_VALUES);
   var key;
-  var stepping = DEBUG_IS_STEPPING(f);
   var value_array = [UNDEFINED];
   while (%SetIteratorNext(iterator, value_array)) {
-    if (stepping) %DebugPrepareStepInIfStepping(f);
     key = value_array[0];
     %_Call(f, receiver, key, key, this);
   }
@@ -431,10 +429,8 @@ function MapForEach(f, receiver) {
   if (!IS_CALLABLE(f)) throw MakeTypeError(kCalledNonCallable, f);
 
   var iterator = new MapIterator(this, ITERATOR_KIND_ENTRIES);
-  var stepping = DEBUG_IS_STEPPING(f);
   var value_array = [UNDEFINED, UNDEFINED];
   while (%MapIteratorNext(iterator, value_array)) {
-    if (stepping) %DebugPrepareStepInIfStepping(f);
     %_Call(f, receiver, value_array[1], value_array[0], this);
   }
 }