ServiceWorker: Collect update check result of scripts

Update check result of each script are collected and stored in
ServiceWorkerVersion. Following patches would use the data to
continue the update process if some script changed.

Bug: 648295
Change-Id: I2c62ab15db1618065199f948e47465530dded870
Reviewed-on: https://chromium-review.googlesource.com/c/1385858
Commit-Queue: Ting Shao <ting.shao@intel.com>
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622379}
9 files changed