Cronet: Make jar_src.py zero-out timestamps

Zero'ed timestamps means the build output is the same for each run,
which is generally desireable.

I checked that these two files were the same before/after:
 * cronet_api-src.jar
 * cronet_impl_common_java-src.jar

Where "the same" means they no longer contain directory entries
and also no "META-INF/MANIFEST.MF" file.

Bug: 383340
Change-Id: I4f644378dc3c33e429010509202011dd7b7f9f95
Reviewed-on: https://chromium-review.googlesource.com/c/1351425
Commit-Queue: agrieve <agrieve@chromium.org>
Reviewed-by: Paul Jensen <pauljensen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612049}
2 files changed