GitLab

- Remove HasSyncingEngine: It just checked "engine_ != nullptr", don't
  need a method for that (and most places already checked the member
  variable directly anyway).
- Make IsSyncAllowedByPlatform private.
- Move is_first_time_sync_configure_ to where it makes more sense.
- Simplify a DCHECK - less negation.
- Remove an unnecessary WeakPtr.
- Merge InitializeEngine into StartUpSlowEngineComponents, its only
  call site.

Bug: 839834
Change-Id: I2bd5a4829a2d7ade3a9acbdfe5c19f7c4f425968
Reviewed-on: https://chromium-review.googlesource.com/1101207Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567583}