[es6] Reintroduce the instanceof operator in the backends.

src/mips/interface-descriptors-mips.cc

Index: src/mips/interface-descriptors-mips.cc
diff --git a/src/mips/interface-descriptors-mips.cc b/src/mips/interface-descriptors-mips.cc
index 58fb181a61225a887bd1322e151336e2045deeb0..30a7a747d8c7a6cc4a19a78fe3beb169f9f37ee9 100644
--- a/src/mips/interface-descriptors-mips.cc
+++ b/src/mips/interface-descriptors-mips.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; }