Input type number should return SpinButtonRole from blink to chromium side to expose w correct role.

This patch would return SpinButtonRole for input type number.
So, that input type attribute "number" could be exposed similar to ARIA role spinbutton.

This is in accordance with following http://rawgit.com/w3c/aria/master/html-aam/html-aam.html

Note: I am facing problem in rebasing this https://codereview.chromium.org/653433002/ CL. So, I'm continuing the same in this new CL.

BUG=385014

Review URL: https://codereview.chromium.org/718433002

git-svn-id: svn://svn.chromium.org/blink/trunk@185056 bbb929c8-8fbe-4397-9dbb-9b2b20218538