[Mojo] Draw GL from within sample_app

This CL replaces hello_world_service with native_viewport in mojo_shell and
sample_app. After this CL, we're able to draw GL from within sample_app.
However, we're still using a bit of a hack to transfer the GL interface to the
sample_app.

R=aa@chromium.org
BUG=none

Review URL: https://codereview.chromium.org/92643002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237659 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237659