Preserve modification timestamp when zipping files.

Files packaged in a zip archive now have their last modification date
and time set. When unzipping the files, the output file's last
modification time is also set (if the time in the zip file is not valid,
the output's file time is not set to prevent the original bug causing
files to have dates set to 1980).

Also fixed some cpplint issues.

BUG=326988
TEST=ZipTest.ZipTimeStamp

Review URL: https://codereview.chromium.org/99333019

Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 0ab84b0c8a685c5ba1ecfe934303b15738e0fe56