This adds support for the InlineTextBox role in the AX tree,
and its attributes.

Depends on this Blink change that adds InlineTextBox support.
https://codereview.chromium.org/23983002/

This change only adds support and makes minimal changes to
allow tests to pass. Other changes will take advantage of the
inline text boxes to compute boundsForRange, etc.

BUG=98977

Review URL: https://codereview.chromium.org/25943003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232429 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 232429