add source changed event stream

BUG=
R=brianwilkerson@google.com

Review URL: https://codereview.chromium.org//737673002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41818 260f80e4-7a28-3924-810f-c04153c831b5
Extract incremental resolver classes into separate files.

R=brianwilkerson@google.com
BUG=

Review URL: https://codereview.chromium.org//743543002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41819 260f80e4-7a28-3924-810f-c04153c831b5
Revert bigint changes of r41817 until dart2js failures are understood and fixed.
Keep x64 assembler additions.

Review URL: https://codereview.chromium.org//741613002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41820 260f80e4-7a28-3924-810f-c04153c831b5