Add SExpression test and share tests between dart2dart and analyzer2dart.

BUG=
R=paulberry@google.com, sigurdm@google.com

Review URL: https://codereview.chromium.org//669673006

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41255 260f80e4-7a28-3924-810f-c04153c831b5
Support unreachable code in blocks in analyzer2dart.

BUG=
R=sigurdm@google.com

Review URL: https://codereview.chromium.org//669693002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41256 260f80e4-7a28-3924-810f-c04153c831b5