Android native accessibility: Decorate link nodes with URLSpans.

This makes talkback recognize the accessibility node as containing a link.

R=dmazzoni@chromium.org
BUG=348184

Review URL: https://codereview.chromium.org/184553009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255854 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255854