New hydrogen instruction to reduce cost of growing an array on keyed stores.

src/runtime/runtime-array.cc

Index: src/runtime/runtime-array.cc
diff --git a/src/runtime/runtime-array.cc b/src/runtime/runtime-array.cc
index 8391f451585e34e4cd4ecd6a1f5e12d520e6121d..4964d238a03a06d85c26eee8358edfeb253ecf25 100644
--- a/src/runtime/runtime-array.cc
+++ b/src/runtime/runtime-array.cc
@@ -1221,7 +1221,7 @@ RUNTIME_FUNCTION(Runtime_NormalizeElements) {
 // GrowArrayElements returns a sentinel Smi if the object was normalized.
 RUNTIME_FUNCTION(Runtime_GrowArrayElements) {
   HandleScope scope(isolate);
-  DCHECK(args.length() == 3);
+  DCHECK(args.length() == 2);
   CONVERT_ARG_HANDLE_CHECKED(JSObject, object, 0);
   CONVERT_SMI_ARG_CHECKED(key, 1);