The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a03dec27a97fbc3263fe802e6aa943876a5783ec

commit a03dec27a97fbc3263fe802e6aa943876a5783ec
Author: Kurt Horimoto <kkhorimoto@chromium.org>
Date: Wed Aug 08 19:49:40 2018

[iOS] Reset FullscreenModel for URL-changing same-document navigations.

This is a heuristic intended to allow the toolbars to be shown when
navigating to an AMP page, assuming that these navigations are coupled
with URL-changing history state updates (i.e. navigating to AMP pages
from the Google search results page).  This is likely too broad of a
condition, and should be updated to include a more robust heuristic that
checks the DOM of loaded iframes for AMP markup.

Bug:  866018 
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I325d4339707e47bb2ae8f1b3c2c83538056be400
Reviewed-on: https://chromium-review.googlesource.com/1166188
Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581666}
[modify] https://crrev.com/a03dec27a97fbc3263fe802e6aa943876a5783ec/ios/chrome/browser/ui/fullscreen/fullscreen_web_state_observer.h
[modify] https://crrev.com/a03dec27a97fbc3263fe802e6aa943876a5783ec/ios/chrome/browser/ui/fullscreen/fullscreen_web_state_observer.mm
[modify] https://crrev.com/a03dec27a97fbc3263fe802e6aa943876a5783ec/ios/chrome/browser/ui/fullscreen/fullscreen_web_state_observer_unittest.mm

First-pass heuristic has landed; setting next action date for canary verification.

The NextAction date has arrived: 2018-08-09

Tested this morning and could no longer repro the bug where navigating to preloaded AMP pages does not show the toolbars.  Requesting merge despite the fact that this wasn't originally marked as RBS since this is a fix that Mardini wants for M69.  The fix will need to be refined in M70, but the CL in comment 3 is a cherry-pickable fix for M69 that brings our behavior in line with that of firefox.

This bug requires manual review: Less than 22 days to go before AppStore submit on M69
Please contact the milestone owner if you have questions.
Owners: amineer@(Android), kariahda@(iOS), cindyb@(ChromeOS), govind@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

I want to understand why this needs to make M69 better than just the fact that Mardini wanted it. Kurt or Gabe, do you have any additional information on this considering Mardini is out  until 8/16 I believe.

Some Google searches (i.e. "news") have specialized search results that are implemented using AMP.  When you tap on one of these search results, the resulting page is loaded in an iframe, so the normal navigation flow that we used to show toolbars for these navigations isn't consistently triggered.  This means that it's possible to navigate to a search result when the toolbars are hidden, then you get stuck on the page without access to the navigation controls to navigate back to the SRP.  This change updates our AMP navigation detection heuristic to handle these preload cases.

Yep, being stuck in an AMP page without an obvious way to navigate back is pretty bad.

Ok thank you. I understand now. We want users to be able to navigate back to their search results. Approved.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6aa290a0d3e009253b640346eb676873f0816ebd

commit 6aa290a0d3e009253b640346eb676873f0816ebd
Author: Kurt Horimoto <kkhorimoto@chromium.org>
Date: Thu Aug 09 21:35:50 2018

[iOS] Reset FullscreenModel for URL-changing same-document navigations.

This is a heuristic intended to allow the toolbars to be shown when
navigating to an AMP page, assuming that these navigations are coupled
with URL-changing history state updates (i.e. navigating to AMP pages
from the Google search results page).  This is likely too broad of a
condition, and should be updated to include a more robust heuristic that
checks the DOM of loaded iframes for AMP markup.

Bug:  866018 
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I325d4339707e47bb2ae8f1b3c2c83538056be400
Reviewed-on: https://chromium-review.googlesource.com/1166188
Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#581666}(cherry picked from commit a03dec27a97fbc3263fe802e6aa943876a5783ec)
Reviewed-on: https://chromium-review.googlesource.com/1169783
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Cr-Commit-Position: refs/branch-heads/3497@{#519}
Cr-Branched-From: 271eaf50594eb818c9295dc78d364aea18c82ea8-refs/heads/master@{#576753}
[modify] https://crrev.com/6aa290a0d3e009253b640346eb676873f0816ebd/ios/chrome/browser/ui/fullscreen/fullscreen_web_state_observer.h
[modify] https://crrev.com/6aa290a0d3e009253b640346eb676873f0816ebd/ios/chrome/browser/ui/fullscreen/fullscreen_web_state_observer.mm
[modify] https://crrev.com/6aa290a0d3e009253b640346eb676873f0816ebd/ios/chrome/browser/ui/fullscreen/fullscreen_web_state_observer_unittest.mm

Verified as per the steps in  Issue 837254  on iPhone X iOS 11.4, iPhone 6 iOS 12 beta8 on 69.0.3497.41 beta