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This infobar will be used in WebLayer when popups are blocked. This CL
componentizes the infobar delegate, and adds support to WebLayer for
showing the infobar.

Bug: 1019922
Change-Id: I21d0f0e40dac6af5f4c8e3d5a4067906f64a009a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2248075Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Reviewed-by: Pavel Yatsuk <pavely@chromium.org>
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#779165}