[es6] Reintroduce the instanceof operator in the backends.

test/cctest/test-asm-validator.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/ast/ast.h"
 #include "src/ast/ast-expression-visitor.h"
 #include "src/ast/scopes.h"
 #include "src/parsing/parser.h"
@@ skipping 1782 matching lines @@
 
 TEST(NeStrict) {
   CHECK_FUNC_ERROR(
       "function bar() { return (0 !== 0)|0; }\n"
       "function foo() { bar(); }",
       "asm: line 1: illegal comparison operator\n");
 }
 
 
 TEST(InstanceOf) {
-  const char* errorMsg = FLAG_harmony_instanceof
-                             ? "asm: line 0: do-expression encountered\n"
-                             : "asm: line 1: illegal comparison operator\n";
-
   CHECK_FUNC_ERROR(
       "function bar() { return (0 instanceof 0)|0; }\n"
       "function foo() { bar(); }",
-      errorMsg);
+      "asm: line 1: illegal comparison operator\n");
 }
 
 
 TEST(InOperator) {
   CHECK_FUNC_ERROR(
       "function bar() { return (0 in 0)|0; }\n"
       "function foo() { bar(); }",
       "asm: line 1: illegal comparison operator\n");
 }
 
@@ skipping 683 matching lines @@
         CHECK_EXPR(BinaryOperation, Bounds(cache.kAsmDouble)) {
           CHECK_VAR(x, Bounds(cache.kAsmDouble));
           CHECK_EXPR(Literal, Bounds(cache.kAsmDouble));
         }
       }
     }
     CHECK_SKIP();
   }
   CHECK_FUNC_TYPES_END
 }