We can reduce boilerplate if we pass the continuation to
some InstructionSelector::Emit.* methods.

Change-Id: I0221f446129cc086122d3f77a00de7d1256d3ee1
bug: v8:7310
Reviewed-on: https://chromium-review.googlesource.com/934454
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51847}