[Android WebAPK] Don't request WebAPK update if WebApkActivity is finished

Previously, if a WebAPK needs to be updated because the WebAPK code is out
of date, but the user dismisses the WebAPK prior to the Web Manifest being
fetched:
1) WebApkUpdateManager#destroy() would cancel WebApkUpdateDataFetcher
AND
2) WebApkUpdateManager would not cancel the WebApkUpdateDataFetcher timeout
  callback.
This would cause Chrome to do an update but with the old Web Manifest data.

This CL changes WebApkUpdateManager#destroy() to cancel the
WebApkUpdateDataFetcher timeout callback

BUG=None
TEST=WebApkUpdateManagerTest.testDontRequestUpdateAfterManagerDestroyed

Change-Id: I216d30ffbd80cdffe77c952ab610e294e4c6a6b8
Reviewed-on: https://chromium-review.googlesource.com/c/1468583
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Peter Kotwicz <pkotwicz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631682}
2 files changed