Add some additional annotations for tracking pub performance.

This also makes pub print more detailed timing information in
--verbose mode.

R=rnystrom@google.com
BUG=20859

Review URL: https://codereview.chromium.org//600293002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41407 260f80e4-7a28-3924-810f-c04153c831b5