AppCache: clean up WeakPtrFactory members in classes with children.

This CL marks AppCache clases with WeakPtrFactory members as final, and
removes WeakPtrFactory members from classes that have subclasses.

The superclasses of AppCache classes with WeakPtrFactory members were
checked for WeakPtrFactory members, resulting in minor cleanups.

This CL does not tackle AppCacheUrlRequestJob, because net:URLRequestJob
(which has a WeakPtrFactory) has 35 subclasses. This case will be
addressed separately.

TBR=kinuko

Change-Id: I04bb0757c34fa03620517d04571cba5a0e4a77a5
Reviewed-on: https://chromium-review.googlesource.com/c/1267337
Commit-Queue: Victor Costan <pwnall@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#601431}
28 files changed