This optimizes ChangeNumberToFloat64/BuildFastLoop for better code generation.

Change-Id: I54c1a07dfe237d4596f91dd6bab7f1d857bdd8a4
Reviewed-on: https://chromium-review.googlesource.com/1180730Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Kanghua Yu <kanghua.yu@intel.com>
Cr-Commit-Position: refs/heads/master@{#55204}