[es6] Reintroduce the instanceof operator in the backends.

src/compiler/code-assembler.h

Index: src/compiler/code-assembler.h
diff --git a/src/compiler/code-assembler.h b/src/compiler/code-assembler.h
index 32fc5e60cb1ac2fe71e951d2f176421f632b2ca4..d32093496bd33f813e56aaecd04e3133f21340ce 100644
--- a/src/compiler/code-assembler.h
+++ b/src/compiler/code-assembler.h
@@ -236,6 +236,9 @@ class CodeAssembler {
   Node* AtomicStore(MachineRepresentation rep, Node* base, Node* index,
                     Node* value);
 
+  // Store a value to the root array.
+  Node* StoreRoot(Heap::RootListIndex root_index, Node* value);
+
 // Basic arithmetic operations.
 #define DECLARE_CODE_ASSEMBLER_BINARY_OP(name) Node* name(Node* a, Node* b);
   CODE_ASSEMBLER_BINARY_OP_LIST(DECLARE_CODE_ASSEMBLER_BINARY_OP)