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  * Observes visibility of the aura window that contains the webview
    and adds a new OnVisible hook when the window is made visible.
  * Requests initial focus when visible.
  * Same OnVisible hook will be used to register IME observers in a
    forthcoming cl.

Bug: internal b/169848935, internal b/161811385
Test: manual on device and with wayland webview client
Change-Id: I37d0dad610f99398363c6b8f91579cb0a42853c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2487700
Commit-Queue: Ryan Daum <rdaum@chromium.org>
Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819648}