[runtime] Optimize and unify rest parameters.

src/x64/interface-descriptors-x64.cc

Index: src/x64/interface-descriptors-x64.cc
diff --git a/src/x64/interface-descriptors-x64.cc b/src/x64/interface-descriptors-x64.cc
index 0fd2b83fd2bb8b4a04ca45851893ee930cf98798..e5940a20896799a2e70c2668343c45840bcda7c0 100644
--- a/src/x64/interface-descriptors-x64.cc
+++ b/src/x64/interface-descriptors-x64.cc
@@ -63,11 +63,6 @@ const Register ArgumentsAccessNewDescriptor::parameter_count() { return rcx; }
 const Register ArgumentsAccessNewDescriptor::parameter_pointer() { return rdx; }
 
 
-const Register RestParamAccessDescriptor::parameter_count() { return rcx; }
-const Register RestParamAccessDescriptor::parameter_pointer() { return rdx; }
-const Register RestParamAccessDescriptor::rest_parameter_index() { return rbx; }
-
-
 const Register ApiGetterDescriptor::function_address() { return r8; }
 
 
@@ -97,6 +92,13 @@ void FastNewContextDescriptor::InitializePlatformSpecific(
 }
 
 
+void FastNewRestParameterDescriptor::InitializePlatformSpecific(
+    CallInterfaceDescriptorData* data) {
+  Register registers[] = {rdi};
+  data->InitializePlatformSpecific(arraysize(registers), registers);
+}
+
+
 void TypeofDescriptor::InitializePlatformSpecific(
     CallInterfaceDescriptorData* data) {
   Register registers[] = {rbx};