Many handlers are not used again, so we can improve the cache hit rate
by caching fewer handlers. Specifically, in this CL, when a StoreIC
miss causes a new map transition to be created, then the handler is not
cached right away yet (it will be cached next time, when the transition
exists already).

Also, fix an embarrassing bug where growing a TransitionArray dropped
cached handlers. That further improves the cache hit rate. ;-)

Bug: chromium:752867, chromium:753819
Change-Id: Id8db5ca1e780a5fe8fc61db7f20996e61c65a90e
Reviewed-on: https://chromium-review.googlesource.com/619851Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47433}