Unify JSEntryStub and JSConstructEntryStub, and some more code stub cleanups.

R=mvstanton@chromium.org

Review URL: https://codereview.chromium.org/545163002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23742 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Harden OptimizeFunctionOnNextCall.

BUG=411237
LOG=N
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/547553003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23743 ce2b1a6d-e550-0410-aec6-3dcde31c8c00