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- -Wfinal-dtor-non-final-class warns on classes with final dtors but
  not final classes.
- Error messages are better when the class is marked final.
- Fix existing issues in code base and a follow up will remove warning
  exemption.

Bug: 999886
Test: no errors building
Change-Id: I6d861d9e63cf93670087e56c80a624d5b69d038c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2468789
Auto-Submit: Zentaro Kavanagh <zentaro@chromium.org>
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817153}