[stubs] Unify (and optimize) implementation of ToObject.

src/collection.js

Index: src/collection.js
diff --git a/src/collection.js b/src/collection.js
index ceab1642c557bf2526a9f3e557afb5d5299061c8..f0bc42392d9b117e3204e0135d2bb621ff248eb3 100644
--- a/src/collection.js
+++ b/src/collection.js
@@ -268,7 +268,7 @@ function SetForEach(f, receiver) {
   while (%SetIteratorNext(iterator, value_array)) {
     if (stepping) %DebugPrepareStepInIfStepping(f);
     key = value_array[0];
-    var new_receiver = needs_wrapper ? $toObject(receiver) : receiver;
+    var new_receiver = needs_wrapper ? TO_OBJECT(receiver) : receiver;
     %_CallFunction(new_receiver, key, key, this, f);
   }
 }
@@ -457,7 +457,7 @@ function MapForEach(f, receiver) {
   var value_array = [UNDEFINED, UNDEFINED];
   while (%MapIteratorNext(iterator, value_array)) {
     if (stepping) %DebugPrepareStepInIfStepping(f);
-    var new_receiver = needs_wrapper ? $toObject(receiver) : receiver;
+    var new_receiver = needs_wrapper ? TO_OBJECT(receiver) : receiver;
     %_CallFunction(new_receiver, value_array[1], value_array[0], this, f);
   }
 }