Insulate portable GZipHelpers code

The helpers are portable code and don't depend on 'base' code,
this fixes a layer violation.

Another advantage is to make it easier to deploy Chromium's zlib i.e.
no need to write your own helpers.

Change-Id: I10a5452dd8835f1e1ec592d7c1c1cc3bb67f9e70
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1742295


Commit-Queue: Adenilson Cavalcanti <cavalcantii@chromium.org>
Reviewed-by: Chris Blume <cblume@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#685673}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 3b866f5cefa5e4d12af1d565ea779e727e4feca6