Optimize trivial regexp disjunctions

test/mjsunit/regress/regress-chromium-482998.js

+// 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.
+
+// Should not time out.  Running time 0.5s vs. 120s before the change.
+function collapse() {
+  var src = "(?:";
+  for (var i = 128; i < 0x1000; i++) {
+    src += "a" + String.fromCharCode(i) + "|";
+  }
+  src += "aa)";
+  var collapsible = new RegExp(src);
+  var subject = "zzzzzzz" + String.fromCharCode(3000);
+  for (var i = 0; i < 1000; i++) {
+    subject += "xxxxxxx";
+  }
+  for (var i = 0; i < 2000; i++) {
+    assertFalse(collapsible.test(subject));
+  }
+}
+
+collapse();