Merged r13733 into 3.16 branch.

Visit stored context when iterating stack for optimized stub.

BUG=v8:2509

R=mstarzinger@chromium.org

Review URL: https://chromiumcodereview.appspot.com/12865003

git-svn-id: https://v8.googlecode.com/svn/branches/3.16@13951 ce2b1a6d-e550-0410-aec6-3dcde31c8c00