GitLab

Create DownloadOfflineContentProviderFactory, a
SimpleKeyedServiceFactory that creates and maintains ownership of
DownloadOfflineContentProviders associated to ProfileKeys.

This gets rid of Android-specific globals and platform-specific
ownership in DownloadCoreServiceImpl.

Change-Id: Iabee9d98f961849ebdfb35c678cf625db605705f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1664995
Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>
Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#671383}