RegExpParser: Fix Reset()ting to the end.

test/mjsunit/regress/regress-3756.js

+// Copyright 2014 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.
+
+(function TestIdentityEscapes() {
+  // \u not followed by 4 hex digits is treated as an identity escape.
+  var r0 = /\u/;
+  assertTrue(r0.test("u"));
+
+  r0 = RegExp("\\u");
+  assertTrue(r0.test("u"));
+
+  var r1 = /\usecond/;
+  assertTrue(r1.test("usecond"));
+
+  r1 = RegExp("\\usecond");
+  assertTrue(r1.test("usecond"));
+
+  var r2 = /first\u/;
+  assertTrue(r2.test("firstu"));
+  // This used to return true (which was a bug).
+  assertFalse(r2.test("first\\u"));
+
+  r2 = RegExp("first\\u");
+  assertTrue(r2.test("firstu"));
+  // This used to return true (which was a bug).
+  assertFalse(r2.test("first\\u"));
+
+  var r3 = /first\usecond/;
+  assertTrue(r3.test("firstusecond"));
+  assertFalse(r3.test("first\\usecond"));
+
+  r3 = RegExp("first\\usecond");
+  assertTrue(r3.test("firstusecond"));
+  assertFalse(r3.test("first\\usecond"));
+
+  var r4 = /first\u123second/;
+  assertTrue(r4.test("firstu123second"));
+  assertFalse(r4.test("first\\u123second"));
+
+  r4 = RegExp("first\\u123second");
+  assertTrue(r4.test("firstu123second"));
+  assertFalse(r4.test("first\\u123second"));
+
+  // \X where X is not a legal escape character is treated as identity escape
+  // too.
+  var r5 = /\a/;
+  assertTrue(r5.test("a"));
+
+  r5 = RegExp("\\a");
+  assertTrue(r5.test("a"));
+
+  var r6 = /\asecond/;
+  assertTrue(r6.test("asecond"));
+
+  r6 = RegExp("\\asecond");
+  assertTrue(r6.test("asecond"));
+
+  var r7 = /first\a/;
+  assertTrue(r7.test("firsta"));
+  assertFalse(r7.test("first\\a"));
+
+  r7 = RegExp("first\\a");
+  assertTrue(r7.test("firsta"));
+  assertFalse(r7.test("first\\a"));
+
+  var r8 = /first\asecond/;
+  assertTrue(r8.test("firstasecond"));
+  assertFalse(r8.test("first\\asecond"));
+
+  r8 = RegExp("first\\asecond");
+  assertTrue(r8.test("firstasecond"));
+  assertFalse(r8.test("first\\asecond"));
+})();