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This behaves similar to DelegatedFrameHost. As discussed in
https://chromium-review.googlesource.com/c/chromium/src/+/1173663,
this implements composition instead of inheritance.

Bug: 859977
Change-Id: Icf5e0c83c4b3789a2173933a26067c6275f62765
Reviewed-on: https://chromium-review.googlesource.com/1186199Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Fady Samuel <fsamuel@chromium.org>
Commit-Queue: Xing Xu <xing.xu@intel.com>
Cr-Commit-Position: refs/heads/master@{#586077}