Where the value we are switching on is a constant, we can just look
through each IfValue case and replace the switch and go straight to
the appropriate case. If no case matches, expect and go to the
IfDefault.

For the (unrealistic) example in the linked bug, this improves
performance ~1.5x.

Bug: v8:7389
Change-Id: I7ffe209bda9ed22571ea106396b18e0bcf9a1e22
Reviewed-on: https://chromium-review.googlesource.com/893141
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51029}