Improvements and tests for top-level variables matching.

It is OK to reorder them.
But it is not OK to change number of them or their types.

R=brianwilkerson@google.com
BUG=

Review URL: https://codereview.chromium.org//719383003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41839 260f80e4-7a28-3924-810f-c04153c831b5