Test-detected breakage: uri, crypto

Updated/moved Uri coverage to dart:core, removed crypto coverage, fixed code, and improved test output.

Staged at:
http://book.dart-lang.appspot.com/docs/dart-up-and-running/contents/ch03.html

Related CL (but review this one instead): https://chromiumcodereview.appspot.com/16276004

I'll update the preface in a separate CL.

Review URL: https://chromiumcodereview.appspot.com/16212009