[es6] Reintroduce the instanceof operator in the backends.

src/parsing/parser-base.h

Index: src/parsing/parser-base.h
diff --git a/src/parsing/parser-base.h b/src/parsing/parser-base.h
index d7ae67e6b353dff421cb49dd104df7fbbba2c990..fce632c7741dd42edaa51170416862cfae224b27 100644
--- a/src/parsing/parser-base.h
+++ b/src/parsing/parser-base.h
@@ -2561,16 +2561,11 @@ ParserBase<Traits>::ParseBinaryExpression(int prec, bool accept_IN,
           case Token::NE_STRICT: cmp = Token::EQ_STRICT; break;
           default: break;
         }
-        if (FLAG_harmony_instanceof && cmp == Token::INSTANCEOF) {
-          x = Traits::RewriteInstanceof(x, y, pos);
-        } else {
-          x = factory()->NewCompareOperation(cmp, x, y, pos);
-          if (cmp != op) {
-            // The comparison was negated - add a NOT.
-            x = factory()->NewUnaryOperation(Token::NOT, x, pos);
-          }
+        x = factory()->NewCompareOperation(cmp, x, y, pos);
+        if (cmp != op) {
+          // The comparison was negated - add a NOT.
+          x = factory()->NewUnaryOperation(Token::NOT, x, pos);
         }
-
       } else if (op == Token::EXP) {
         x = Traits::RewriteExponentiation(x, y, pos);
       } else {