Incremental compiler detects when library graph changes.

Also, don't suppress all exceptions as it hid errors in the test.

R=johnniwinther@google.com

Review URL: https://codereview.chromium.org//796353003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42505 260f80e4-7a28-3924-810f-c04153c831b5
Incremental compilation of libraries with multiple parts.

R=johnniwinther@google.com

Review URL: https://codereview.chromium.org//815123002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42506 260f80e4-7a28-3924-810f-c04153c831b5