[es6] Reintroduce the instanceof operator in the backends.

src/interface-descriptors.cc

Index: src/interface-descriptors.cc
diff --git a/src/interface-descriptors.cc b/src/interface-descriptors.cc
index c0a342c87e60c63152b01a5823bd5696d3034278..860ad2afd139c7e5a1fd224e389335e8cc549bad 100644
--- a/src/interface-descriptors.cc
+++ b/src/interface-descriptors.cc
@@ -178,13 +178,6 @@ void StoreGlobalViaContextDescriptor::InitializePlatformSpecific(
 }
 
 
-void InstanceOfDescriptor::InitializePlatformSpecific(
-    CallInterfaceDescriptorData* data) {
-  Register registers[] = {LeftRegister(), RightRegister()};
-  data->InitializePlatformSpecific(arraysize(registers), registers);
-}
-
-
 void StringCompareDescriptor::InitializePlatformSpecific(
     CallInterfaceDescriptorData* data) {
   Register registers[] = {LeftRegister(), RightRegister()};