Revert of [builtins] Move StringIncludes to a builtin.

src/js/string.js

Index: src/js/string.js
diff --git a/src/js/string.js b/src/js/string.js
index e0ee7adef769f28a9499a44642510fa4df84dda3..28e74a50cb1fb28af37f9ec63aef39d031fcd423 100644
--- a/src/js/string.js
+++ b/src/js/string.js
@@ -433,6 +433,34 @@
 %FunctionSetLength(StringEndsWith, 1);
 
 
+// ES6 draft 04-05-14, section 21.1.3.6
+function StringIncludes(searchString, position) {  // length == 1
+  CHECK_OBJECT_COERCIBLE(this, "String.prototype.includes");
+
+  var string = TO_STRING(this);
+
+  if (IsRegExp(searchString)) {
+    throw %make_type_error(kFirstArgumentNotRegExp, "String.prototype.includes");
+  }
+
+  searchString = TO_STRING(searchString);
+  var pos = TO_INTEGER(position);
+
+  var stringLength = string.length;
+  if (pos < 0) pos = 0;
+  if (pos > stringLength) pos = stringLength;
+  var searchStringLength = searchString.length;
+
+  if (searchStringLength + pos > stringLength) {
+    return false;
+  }
+
+  return %StringIndexOf(string, searchString, pos) !== -1;
+}
+
+%FunctionSetLength(StringIncludes, 1);
+
+
 // ES6 Draft 05-22-2014, section 21.1.3.3
 function StringCodePointAt(pos) {
   CHECK_OBJECT_COERCIBLE(this, "String.prototype.codePointAt");
@@ -491,6 +519,7 @@
   "codePointAt", StringCodePointAt,
   "concat", StringConcat,
   "endsWith", StringEndsWith,
+  "includes", StringIncludes,
   "match", StringMatchJS,
   "repeat", StringRepeat,
   "replace", StringReplace,