Otherwise we can end up with performance regression with a lot of
frames in cache. Map requires log(N) for lookup, unordered map for
frames ids requires - ~O(1).

R=dgozman@chromium.org

Bug: v8:7078
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Iac1ff7e35daede8c5ebd424f686a8ef8dbae9061
Reviewed-on: https://chromium-review.googlesource.com/767035
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49369}