Port ab9ac994

Original Commit Message:

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

R=mvstanton@chromium.org, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: Ia9ddd0dcf5d6115ee9f8c35e1b05c10f9f0c4b39
Reviewed-on: https://chromium-review.googlesource.com/959441
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Reviewed-by: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#51948}