[Nav Experiment] Set virtual URL for restore session URL.

This removes flicker in Omnibox that briefly exposes the internal URL
when restoring session history. Virtual URL must be set on the pending
item before calling |loadCurrentURLInWebView| because
WebStateObserver::DidStartLoading event fires during this call, which
triggers ToolbarModelDelegateIOS to update itself using the virtual
URL of the pending item.

Bug: 815248
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I260e251d90ad832120b908a61843fe30df261be3
Reviewed-on: https://chromium-review.googlesource.com/1003252
Commit-Queue: Danyao Wang <danyao@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550184}

ios/web/navigation/navigation_manager_impl.mm

@@ -267,6 +267,9 @@ void NavigationManagerImpl::LoadURLWithParams(
         last_committed_url.EqualsIgnoringRef(pending_url)) {
       pending_item->SetIsCreatedFromHashChange(true);
     }
+
+    if (params.virtual_url.is_valid())
+      pending_item->SetVirtualURL(params.virtual_url);
   }
 
   // Add additional headers to the NavigationItem before loading it in the web

ios/web/navigation/wk_based_navigation_manager_impl.mm

@@ -446,10 +446,11 @@ void WKBasedNavigationManagerImpl::Restore(
   // For now, use RELOAD because restoring history is kind of like a reload of
   // the current page.
   params.transition_type = ui::PAGE_TRANSITION_RELOAD;
-  LoadURLWithParams(params);
 
   // This pending item will become the first item in the restored history.
-  GetPendingItemImpl()->SetVirtualURL(items[0]->GetVirtualURL());
+  params.virtual_url = items[0]->GetVirtualURL();
+
+  LoadURLWithParams(params);
 }
 
 void WKBasedNavigationManagerImpl::LoadIfNecessary() {

ios/web/public/navigation_manager.h

@@ -51,6 +51,9 @@ class NavigationManager {
     // The URL to load. Must be set.
     GURL url;
 
+    // The URL to display in Omnibox. If empty, |url| will be displayed.
+    GURL virtual_url;
+
     // The referrer for the load. May be empty.
     Referrer referrer;