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This commit does a few things:

- merges the Chrome AppListViewDelegate into AppListClientImpl;
- cleans up unused references;
- updates methods to proper accesses.

Ownership of major classes:

- Each user has its own AppListSyncableService, and it holds its own
  AppListModelUpdater, ModelBuilders, etc.
- There's only one AppListClientImpl in ChromeBrowserMainExtraPartsAsh
  shared by all users, and it holds Search classes, a mojo pointer to
  the AppListControllerImpl in Ash, etc.
- There's only one singleton AppListServiceImpl shared by all users, and
  it holds AppListControllerDelegateImpl.

Their lifecycles:

- Among these classes, AppListClientImpl is the first to be initiated, in
  PreProfileInit. It binds to AppListController in Ash, and then tells
  AppListServiceImpl two pointers (AppListController*, AppListClientImpl*).
- When AppListServiceImpl receives the two pointers, it should have been
  initiated as a singleton.
- The AppListClientImpl is associated with the current active user profile
  when it's accessed from AppListServiceImpl.

Bug: 733662
Change-Id: Iac6de011185bf88c4b3c575871b69bd7a67c340b
Reviewed-on: https://chromium-review.googlesource.com/974660Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Jiaquan He <hejq@google.com>
Cr-Commit-Position: refs/heads/master@{#546247}