3.22 branch: Fix polymorphic inlined calls with migrating prototypes.

This is a hand-crafted, trimmed-down back-merge version of r18307, fixing just
the issue at hand instead of doing the full refactoring/yak-shaving.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/132123003

git-svn-id: https://v8.googlecode.com/svn/branches/3.22@18527 ce2b1a6d-e550-0410-aec6-3dcde31c8c00