[es6] Reintroduce the instanceof operator in the backends.

src/mips64/interface-descriptors-mips64.cc

Index: src/mips64/interface-descriptors-mips64.cc
diff --git a/src/mips64/interface-descriptors-mips64.cc b/src/mips64/interface-descriptors-mips64.cc
index bc4af563456d6d630a49b0826aad9ab0e4ceab1e..67bae366992ff516f6fc926157d32eea71cdbb86 100644
--- a/src/mips64/interface-descriptors-mips64.cc
+++ b/src/mips64/interface-descriptors-mips64.cc
@@ -46,10 +46,6 @@ const Register StoreGlobalViaContextDescriptor::SlotRegister() { return a2; }
 const Register StoreGlobalViaContextDescriptor::ValueRegister() { return a0; }
 
 
-const Register InstanceOfDescriptor::LeftRegister() { return a1; }
-const Register InstanceOfDescriptor::RightRegister() { return a0; }
-
-
 const Register StringCompareDescriptor::LeftRegister() { return a1; }
 const Register StringCompareDescriptor::RightRegister() { return a0; }