Mutating the descriptor array and the layout descriptor of a map
races with the concurrent marking. This patch simply transfers
ownership of the descriptor array without mutating the map.

Since the old map is not going to be used anymore and there are
not transitions from the old map, this should be safe for trimming
the descriptor arrays during GC.

This patch also adds checks in IC code avoid caching of dummy
transitions from the abandoned prototype map.

Bug: chromium:752461
Change-Id: I7b44ba7c369199bdb3ff48235226fe504c7eb4a5
Reviewed-on: https://chromium-review.googlesource.com/602210
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47275}