INPUT pattern attribute: Enable "unicode" flag.

Pass UTF16 flag to ScriptRegexp. Additional changes:

* ScriptRegexp records an exception message from V8 in order to show friendly
  console errors.
* BaseTextInputType caches ScripRegexp to avoid to show same console errors
  repeatedly.
* Move BaseTextInputType constructor and destructor to .cpp file to avoid to
  include ScriptRegexp.h in BaseTextInputType.h.

Intent-to-ship:
https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/XUNMtri0tI4/qIsHgTWNAQAJ

BUG=535441

Review-Url: https://codereview.chromium.org/2037553002
Cr-Commit-Position: refs/heads/master@{#397352}
7 files changed