In Liftoff, we want to trace the cache state basically before or after
processing each instruction. Instead of duplicating this code
everywhere, introduce a new interface method {NextInstruction}, which
is called before each instruction.

R=titzer@chromium.org

Bug: v8:6600
Change-Id: Iea61738d200076690a8440a75a2fd90018efa43b
Reviewed-on: https://chromium-review.googlesource.com/852457
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50447}