Start the move of launcher_types.h to shelf.

I decided to split the constants into its own component to make the
transition easier to do and review.

BUG=248353
TEST=None, no functional changes
R=jamescook@chromium.org,harrym@chromium.org
TBR=tapted@chromium.org # for c/b/ui/apps

Review URL: https://codereview.chromium.org/97983003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242588 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242588