Reland "[Nav Experiment] Fix broken WebStateObserverTest.IframeNavigation."

This is a reland of a1b00bf181dd7ee4a636cc3e1f678e99223f5466

Original change's description:
> [Nav Experiment] Fix broken WebStateObserverTest.IframeNavigation.
> 
> The test expectations added for RequestInfo were always broken, but it
> was not discovered because slim-nav was not run on CQ.
> 
> Bug: 851119
> Change-Id: Ia9949553d9a0b97cb16a8435b5f8c95084ab1880
> Reviewed-on: https://chromium-review.googlesource.com/c/1369004
> Reviewed-by: Eugene But <eugenebut@chromium.org>
> Commit-Queue: Danyao Wang <danyao@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#615131}

Bug: 851119
Change-Id: I8bb26c31d4164e29dce171a0d118672975551946
Reviewed-on: https://chromium-review.googlesource.com/c/1370194
Commit-Queue: Danyao Wang <danyao@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615250}
1 file changed