This CL adds support for indirect calls.

R=titzer@chromium.org

Bug: v8:6600
Change-Id: Ia29b87fa1f7be873cd722f934b8007c38794dceb
Reviewed-on: https://chromium-review.googlesource.com/877884
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50756}