Migrate DBus service constants from flimflam namespace to shill namespace.

All shill DBus service constants have been moved from the flimflam namespace to
the shill namespace. This CL makes the corresponding changes on the Chrome
side.

Related CLs:
  https://chromium-review.googlesource.com/#/c/170123/
  https://chromium-review.googlesource.com/#/c/170205/
  https://chromium-review.googlesource.com/#/c/170206/
  https://chromium-review.googlesource.com/#/c/170207/
  https://chromium-review.googlesource.com/#/c/170208/
  https://chromium-review.googlesource.com/#/c/170209/
  https://chromium-review.googlesource.com/#/c/170223/
  https://chromium-review.googlesource.com/#/c/170230/
  https://chromium-review.googlesource.com/#/c/170231/

BUG=295425
R=mnissler@chromium.org,pneubeck@chromium.org

Review URL: https://chromiumcodereview.appspot.com/24347002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224715 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 224715
Add a string for a link to the Help Center on the Playpen Learn More page.

This string is not yet used, pending UX discussion and creation of the HC
content.

BUG=296889
R=akuegel@chromium.org

Review URL: https://codereview.chromium.org/24266006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@224716 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 224716