Linux: provide /usr/bin/google-chrome using Debian Alternatives

This will also give us good path forward when enabling SxS
to allow the user to choose where google-chrome points to
(which channel).

BUG=300144
R=mmoss@chromium.org

Review URL: https://codereview.chromium.org/25121005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226270 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226270