fix failing test (TBR)

Review URL: https://codereview.chromium.org//781843003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42128 260f80e4-7a28-3924-810f-c04153c831b5
Rename legacy path library in tools/testing to avoid name collision.

BUG=
R=ricow@google.com

Review URL: https://codereview.chromium.org//756423003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42129 260f80e4-7a28-3924-810f-c04153c831b5