Revert "Make Comparable generic."
Revert "Make Comparable generic."

This reverts commit dd714db881a0ad63eaa1e5491e93dd8843eb5929.

R=lrn@google.com
BUG=

Review URL: https://codereview.chromium.org//12298027

git-svn-id: 29b42837285a5fdcb6c8ad0409bff8538fc60ed2@18657 260f80e4-7a28-3924-810f-c04153c831b5

astashov/logging,dart-lang/logging