This makes sure that frames representing builtin stub continuations not
only materialize all stack slots, but also spilled register values. Note
that this also applies when the stub frame is not the top-most frame.

R=jarin@chromium.org
TEST=mjsunit/regress/regress-6907
BUG=v8:6907

Change-Id: I01a2edf5629de6aac61ceea350d1ab5f91dc2dc1
Reviewed-on: https://chromium-review.googlesource.com/707245Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48415}