Optimize the typeof operator.

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 0cef86e1021070a826381b2a4358ace7817425a2..6e37aeba3af62b7e08ba28c5e21fe8e23b88ead9 100644
--- a/src/x64/interface-descriptors-x64.cc
+++ b/src/x64/interface-descriptors-x64.cc
@@ -68,6 +68,12 @@ void FastNewContextDescriptor::Initialize(CallInterfaceDescriptorData* data) {
 }
 
 
+void TypeofDescriptor::Initialize(CallInterfaceDescriptorData* data) {
+  Register registers[] = {rsi, rbx};
+  data->Initialize(arraysize(registers), registers, NULL);
+}
+
+
 void ToNumberDescriptor::Initialize(CallInterfaceDescriptorData* data) {
   // ToNumberStub invokes a function, and therefore needs a context.
   Register registers[] = {rsi, rax};