Use the new introduced block's reachable flag.
Use the new introduced block's reachable flag.

BUG=
R=verwaest@chromium.org

Review URL: https://chromiumcodereview.appspot.com/26459002

Patch from Weiliang Lin <weiliang.lin2@gmail.com>.

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@17129 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh