[Nav Experiment] Create pending back/forward item in decidePolicy.

WKBackForwardList is updated before navigation delegates are called on
back/forward navigations. This creates a window between decidePolicy
and didStartProvisionalNavigation where WKBasedNavigationManager
incorrectly identifies WKBackForwardList.currentItem as last committed,
even though it is really the pending item. Creating the pending item
in decidePolicy delegate fixes this problem.

Bug: 842151
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I3252edd1def6d0d2eb1499602e05058c3b2fd3b1
Reviewed-on: https://chromium-review.googlesource.com/1142142
Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Commit-Queue: Danyao Wang <danyao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576212}
1 file changed