[Android WebAPK] Send share target information in WebAPK updates

This CL plumbs through share target information for WebAPK updates.

Chromium detects Web Manifest updates (including Web Manifest share
target updates) and requests an update.
Currently, depending on whether the Web Manifest is for an intranet
site, the updated WebAPK would either:
- no longer be able handle share intents (even if the Web Manifest
  share target information was not deleted)
- be created with the same share intent handlers as the current WebAPK
  (regardless of whether the Web Manifest share target information has
   changed).

This CL plumbs through the share target information from
WebApkUpdateDataFetcher#onDataAvailable() to
WebApkUpdateManager::StoreWebApkUpdateRequestToFile()

BUG=912945

Change-Id: Ie416570533abc848eeb23de8c197b44f2a1fd028
Reviewed-on: https://chromium-review.googlesource.com/c/1369709
Commit-Queue: Peter Kotwicz <pkotwicz@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616429}