Use the stack_trace library in scheduled_test.

This also adds a couple features to stack_trace.

Review URL: https://codereview.chromium.org//13157004

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/stack_trace@20752 260f80e4-7a28-3924-810f-c04153c831b5