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

src/interface-descriptors.cc

Index: src/interface-descriptors.cc
diff --git a/src/interface-descriptors.cc b/src/interface-descriptors.cc
index 4c7a1159b53b0e4706c1af307e319ccae2469538..a9b234bfb8fa11fabc65bfe1c2bb5a9cb4fe9447 100644
--- a/src/interface-descriptors.cc
+++ b/src/interface-descriptors.cc
@@ -149,8 +149,7 @@ void ContextOnlyDescriptor::Initialize(CallInterfaceDescriptorData* data) {
 
 void GrowArrayElementsDescriptor::Initialize(
     CallInterfaceDescriptorData* data) {
-  Register registers[] = {ContextRegister(), ObjectRegister(), KeyRegister(),
-                          CapacityRegister()};
+  Register registers[] = {ContextRegister(), ObjectRegister(), KeyRegister()};
   data->Initialize(arraysize(registers), registers, NULL);
 }
 }