Not sure what the right fix for this should be, as the CRWWebControllerContainerView doesn't allow setting the content padding for transient views.  I think we'd have to resize the entire WebState->GetView() to be the space between the toolbars.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8c6e50ac487f07bc090d3272c7f19ac81a49e230

commit 8c6e50ac487f07bc090d3272c7f19ac81a49e230
Author: Kurt Horimoto <kkhorimoto@chromium.org>
Date: Thu Jun 21 16:49:52 2018

[iOS] Provide collapsed and expanded toolbar heights to FullscreenModel.

MoveContentBelowHeader() was not working correctly with the UI refresh
flag enabled because it only knew about the height delta, while we
actually needed to inset based on the expanded height.  This CL updates
the broadcaster API to send the collapsed and expanded toolbar heights
so that this information is available for these content adjustments.

This CL also updates CRWWebViewContentView to check against the old
value of self.contentInset rather than the |_contentInset| ivar.  This
fixes the bug where navigating back from a pdf wouldn't correctly
reset WKScrollView.contentInset since the value of |_contentInset| had
not changed from the previous value.

Bug: 849132,  851129 
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I1e46e4fc69fc0ac7a7d114b7c463e1f6a90964f9
Reviewed-on: https://chromium-review.googlesource.com/1094480
Commit-Queue: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569304}
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/broadcaster/chrome_broadcast_observer.h
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/broadcaster/chrome_broadcast_observer_bridge.h
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/broadcaster/chrome_broadcast_observer_bridge.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/broadcaster/chrome_broadcast_observer_bridge_unittest.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/browser_view_controller.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/fullscreen/fullscreen_content_adjustment_util.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/fullscreen/fullscreen_controller_impl.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/fullscreen/fullscreen_egtest.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/fullscreen/fullscreen_model.h
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/fullscreen/fullscreen_model.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/fullscreen/fullscreen_model_unittest.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/fullscreen/test/fullscreen_model_test_util.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/toolbar/legacy_toolbar_ui_updater.h
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/toolbar/legacy_toolbar_ui_updater.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/toolbar/legacy_toolbar_ui_updater_unittest.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/toolbar/test/test_toolbar_ui_observer.h
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/toolbar/test/test_toolbar_ui_observer.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/toolbar/test/toolbar_broadcast_test_util.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/toolbar/toolbar_ui.h
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/toolbar/toolbar_ui.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/chrome/browser/ui/toolbar/toolbar_ui_broadcasting_util.mm
[modify] https://crrev.com/8c6e50ac487f07bc090d3272c7f19ac81a49e230/ios/web/web_state/ui/crw_web_view_content_view.mm

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4

commit 8a937cfdab8fc8b0743cf5a5df627bde741ac1b4
Author: Gauthier Ambard <gambard@chromium.org>
Date: Wed Jun 27 08:38:50 2018

[iOS Fullscreen] Fix MoveContentBelowHeader

This CL fixes MoveContentBelowHeader to have it take into account the
bottom toolbar. This function now moves the content below the header but
also add an inset for the bottom toolbar.

Bug:  851129 
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I2b7c5e54e1597bf2779e028381b9d05910c021c7
Reviewed-on: https://chromium-review.googlesource.com/1111845
Reviewed-by: Mark Cogan <marq@chromium.org>
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570697}
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/broadcaster/chrome_broadcast_observer.h
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/broadcaster/chrome_broadcast_observer_bridge.h
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/broadcaster/chrome_broadcast_observer_bridge.mm
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/browser_view_controller.mm
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/fullscreen/fullscreen_content_adjustment_util.mm
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/fullscreen/fullscreen_controller_impl.mm
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/fullscreen/fullscreen_model.h
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/fullscreen/fullscreen_model.mm
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/toolbar/legacy_toolbar_ui_updater.h
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/toolbar/legacy_toolbar_ui_updater.mm
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/toolbar/legacy_toolbar_ui_updater_unittest.mm
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/toolbar/test/test_toolbar_ui_observer.h
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/toolbar/test/test_toolbar_ui_observer.mm
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/toolbar/toolbar_ui.h
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/toolbar/toolbar_ui.mm
[modify] https://crrev.com/8a937cfdab8fc8b0743cf5a5df627bde741ac1b4/ios/chrome/browser/ui/toolbar/toolbar_ui_broadcasting_util.mm

Verified in 69.0.3480.0 Canary, iPhone X  iOS 11.4.
Looks good

The NextAction date has arrived: 2018-07-04