[Atomics] Make Atomics.compareExchange a builtin using TF

src/js/harmony-atomics.js

Index: src/js/harmony-atomics.js
diff --git a/src/js/harmony-atomics.js b/src/js/harmony-atomics.js
index 16a4aae69ab3ebd4750b533905de1f60f533d61b..fbdf3c0457a2d8c921732e9a285219d31d43be30 100644
--- a/src/js/harmony-atomics.js
+++ b/src/js/harmony-atomics.js
@@ -52,14 +52,6 @@ function ValidateIndex(index, length) {
 
 //-------------------------------------------------------------------
 
-function AtomicsCompareExchangeJS(sta, index, oldValue, newValue) {
-  CheckSharedIntegerTypedArray(sta);
-  index = ValidateIndex(index, %_TypedArrayGetLength(sta));
-  oldValue = TO_NUMBER(oldValue);
-  newValue = TO_NUMBER(newValue);
-  return %_AtomicsCompareExchange(sta, index, oldValue, newValue);
-}
-
 function AtomicsAddJS(ia, index, value) {
   CheckSharedIntegerTypedArray(ia);
   index = ValidateIndex(index, %_TypedArrayGetLength(ia));
@@ -138,7 +130,6 @@ var Atomics = global.Atomics;
 utils.InstallFunctions(Atomics, DONT_ENUM, [
   // TODO(binji): remove the rest of the (non futex) Atomics functions as they
   // become builtins.
-  "compareExchange", AtomicsCompareExchangeJS,
   "add", AtomicsAddJS,
   "sub", AtomicsSubJS,
   "and", AtomicsAndJS,