Update timestmap of file only when content is changed

This can reduce build steps in incremental build.

I also changed AtomicOutput to avoid some error on windows.

Bug: 810298
Change-Id: I6d076a70b7273bada7e6a94afbd7d805de4b89c2
Reviewed-on: https://chromium-review.googlesource.com/1127510
Reviewed-by: Ken Rockot <rockot@chromium.org>
Reviewed-by: Eric Stevenson <estevenson@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573123}
3 files changed