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This CL adds showing of the (now-componentized) ads blocked infobar in
WebLayer. This presentation is made in //weblayer's
SubresourceFilterClientImpl as directed by
//components/subresource_filter. The implementation is adapted from
that of //chrome's ChromeSubresourceFilterClient, but simplified:
- We leave interaction with content settings for followup work
- We do not track whether the infobar has previously been shown for the
  current navigation. The reason is that
  ContentSubresourceFilterThrottleManager already does such tracking
  itself in its MaybeShowNotification() method, so the client should
  never actually receive a duplicate request to show a notification for
  a given navigation.

We also add a browsertest that the infobar is presented when a resource
is blocked and is removed when navigating away from the page with a
blocked resource. Note that while it would be useful to also add tests
in Java, we can't at this time due to crbug.com/899903.

We leave implementation of the reload functionality that the user can
trigger via the infobar for a followup CL.

Bug: 1116095
Change-Id: Icb182143b0d27de5f03efc88ce8013be3c5c91d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2563549
Commit-Queue: Colin Blundell <blundell@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833308}