[iOS] Refactor CBDCollectionView initialization

-Add another initializer to ClearBrowsingDataCollectionViewController,
so to allow dependency injection in tests.
-Make corrections on ClearBrowsingDataManager, to avoid a strong
reference cycle.
-Change tests to utilise more appropriate methods.

Bug: 935350
Change-Id: I2d4a1b3a740a75785499f3487ee94b842949ce0e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1579719
Reviewed-by: Mark Cogan <marq@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Huanzhong Huang <huanzhong@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653549}
6 files changed