Use a more compact internal representation for FileSpan.

R=rnystrom@google.com

Review URL: https://codereview.chromium.org//706133002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41591 260f80e4-7a28-3924-810f-c04153c831b5
Add missing StorePointer/StoreSmi in ContextScope.

R=iposva@google.com

Review URL: https://codereview.chromium.org//673253002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41592 260f80e4-7a28-3924-810f-c04153c831b5