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This CL moves AppBanner* code from:
  chrome/android/banners
... to ...
  chrome/browser/banners/android
... and modularizes it in the process.

Bug: 1135551
Change-Id: I8773b293e55f03ca66da15551e27a06e26e2ae96
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2489917
Commit-Queue: Finnur Thorarinsson <finnur@chromium.org>
Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821646}