Make `String.prototype.{starts,ends}With` throw when passing a regular expression

src/harmony-string.js

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 46 matching lines @@
 
 
 // ES6 draft 07-15-13, section 15.5.3.22
 function StringStartsWith(searchString /* position */) {  // length == 1
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["String.prototype.startsWith"]);
   }
 
   var s = TO_STRING_INLINE(this);
+
+  if (IS_REGEXP(searchString)) {
+    throw MakeTypeError("first_argument_not_regexp",
+                        ["String.prototype.startsWith"]);
+  }
+
   var ss = TO_STRING_INLINE(searchString);
   var pos = 0;
   if (%_ArgumentsLength() > 1) {
     pos = %_Arguments(1);  // position
     pos = ToInteger(pos);
   }
 
   var s_len = s.length;
   var start = MathMin(MathMax(pos, 0), s_len);
   var ss_len = ss.length;
   if (ss_len + start > s_len) {
     return false;
   }
 
   return %StringIndexOf(s, ss, start) === start;
 }
 
 
 // ES6 draft 07-15-13, section 15.5.3.23
 function StringEndsWith(searchString /* position */) {  // length == 1
   if (IS_NULL_OR_UNDEFINED(this) && !IS_UNDETECTABLE(this)) {
     throw MakeTypeError("called_on_null_or_undefined",
                         ["String.prototype.endsWith"]);
   }
 
   var s = TO_STRING_INLINE(this);
+
+  if (IS_REGEXP(searchString)) {
+    throw MakeTypeError("first_argument_not_regexp",
+                        ["String.prototype.endsWith"]);
+  }
+
   var ss = TO_STRING_INLINE(searchString);
   var s_len = s.length;
   var pos = s_len;
   if (%_ArgumentsLength() > 1) {
     var arg = %_Arguments(1);  // position
     if (!IS_UNDEFINED(arg)) {
       pos = ToInteger(arg);
     }
   }
 
@@ skipping 42 matching lines @@
   // Set up the non-enumerable functions on the String prototype object.
   InstallFunctions($String.prototype, DONT_ENUM, $Array(
     "repeat", StringRepeat,
     "startsWith", StringStartsWith,
     "endsWith", StringEndsWith,
     "contains", StringContains
   ));
 }
 
 ExtendStringPrototype();