Flush file content to disk before diffing files,
may cause unpredictable results on Windows.

Convert from \r\n to \n when comparing diff result.

Change-Id: Ibcd6154a2382dba1338ee5674333611aea16bb65
Reviewed-on: https://go-review.googlesource.com/36750Reviewed-by: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>