Use asynchronous spellchecking in spelling-hasspellingmarker.js

Refactoring spelling-hasspellingmarker.js to use asynchronous spellchecking.
In addition, adds some bits for non-DumpRenderTree users.

It's based on WebKit changeset: http://trac.webkit.org/changeset/164100

BUG=295722

Review URL: https://codereview.chromium.org/204383002

git-svn-id: svn://svn.chromium.org/blink/trunk@169636 bbb929c8-8fbe-4397-9dbb-9b2b20218538