Roll back "Use package:stack_trace in unittest."
Roll back "Use package:stack_trace in unittest."

This reverts r24652, r24659, and r24661. r24652 triggered a crashing bug in all
the Dartium tests, so it's being reverted until that bug is fixed.

BUG=11649
R=asiva@google.com

Review URL: https://codereview.chromium.org//18400002

git-svn-id: a962b240025cf0577aa172e20f49ccb159ba6be1@24669 260f80e4-7a28-3924-810f-c04153c831b5

cjkao/dart-pub,maxwellpeterson-wf/pub,computmaxer/pub,dart-lang/pub,dart-lang/pub