This also refactors CodeAssembler::Branch(condition,true_label,false_label)
to support constant folding, and adds Branch(condition,true_label,false_body)
variants for special cases.

Change-Id: Ifc04442657295124a95c60f76efde5c46de6f1b5
Reviewed-on: https://chromium-review.googlesource.com/1186136
Commit-Queue: Kanghua Yu <kanghua.yu@intel.com>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55372}