[rAC] Ensure proper keyboard navigation.

BaseView blocks all keyDown:/keyUp: messages, but keyboard navigation
relies on those messages travelling along the responder chain. This
change makes sure that the BaseView subclass simply forwards all key
messages to its next responder.

NOTRY=true
BUG=286524

Review URL: https://codereview.chromium.org/24170004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225806 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225806