This addresses the odd performance cliff, where the CallIC tracks known
JSFunction targets, but goes MEGAMORPHIC when it sees a JSBoundFunction
target. With this fix in place the micro-benchmark on the bug goes from

  arrowCall: 82 ms.
  boundCall: 234 ms.

to

  arrowCall: 81 ms.
  boundCall: 80 ms.

so Function#bind doesn't cause any additional overhead anymore.

Bug: v8:5267, v8:6962
Change-Id: Iaceaf89fd3e99e2afe2ae45e96a6813a3ef8b1d2
Reviewed-on: https://chromium-review.googlesource.com/727879
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48722}