Revert of [runtime] Remove useless IN builtin.

src/runtime.js

 // Copyright 2006-2008 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.
 
 // This files contains runtime support implemented in JavaScript.
 
 // CAUTION: Some of the functions specified in this file are called
 // directly from compiled code. These are the functions with names in
 // ALL CAPS. The compiled code passes the first argument in 'this'.
 
@@ skipping 26 matching lines @@
 var BIT_AND;
 var BIT_AND_STRONG;
 var BIT_XOR;
 var BIT_XOR_STRONG;
 var SHL;
 var SHL_STRONG;
 var SAR;
 var SAR_STRONG;
 var SHR;
 var SHR_STRONG;
+var IN;
 var INSTANCE_OF;
 var CALL_NON_FUNCTION;
 var CALL_NON_FUNCTION_AS_CONSTRUCTOR;
 var CALL_FUNCTION_PROXY;
 var CALL_FUNCTION_PROXY_AS_CONSTRUCTOR;
 var CONCAT_ITERABLE_TO_ARRAY;
 var APPLY_PREPARE;
 var REFLECT_APPLY_PREPARE;
 var REFLECT_CONSTRUCT_PREPARE;
 var STACK_OVERFLOW;
@@ skipping 418 matching lines @@
   }
   throw %MakeTypeError(kStrongImplicitConversion);
 }
 
 
 /* -----------------------------
    - - -   H e l p e r s   - - -
    -----------------------------
 */
 
+// ECMA-262, section 11.8.7, page 54.
+IN = function IN(x) {
+  if (!IS_SPEC_OBJECT(x)) {
+    throw %MakeTypeError(kInvalidInOperatorUse, this, x);
+  }
+  if (%_IsNonNegativeSmi(this)) {
+    if (IS_ARRAY(x) && %_HasFastPackedElements(x)) {
+      return this < x.length;
+    }
+    return %HasElement(x, this);
+  }
+  return %HasProperty(x, %$toName(this));
+}
+
+
 // ECMA-262, section 11.8.6, page 54. To make the implementation more
 // efficient, the return value should be zero if the 'this' is an
 // instance of F, and non-zero if not. This makes it possible to avoid
 // an expensive ToBoolean conversion in the generated code.
 INSTANCE_OF = function INSTANCE_OF(F) {
   var V = this;
   if (!IS_SPEC_FUNCTION(F)) {
     throw %MakeTypeError(kInstanceofFunctionExpected, F);
   }
 
@@ skipping 417 matching lines @@
 $toBoolean = ToBoolean;
 $toInteger = ToInteger;
 $toLength = ToLength;
 $toName = ToName;
 $toNumber = ToNumber;
 $toPositiveInteger = ToPositiveInteger;
 $toPrimitive = ToPrimitive;
 $toString = ToString;
 
 })