[Nav Experiment] Do not notify OnPageLoaded for restore_session.html.

When switching to an evicted tab, WKBasedNavigationManager loads
restore_session.html to restore back/forward history. This load should
not be counted as a new page load by TabUsageRecorder.

This fixes TabUsageRecorderTestCase/testEvictedTabReloadBackground.

Bug: 807428
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: If194acd0de633bc170f221d8a960514995425bce
Reviewed-on: https://chromium-review.googlesource.com/917524Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Danyao Wang <danyao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536743}

ios/web/web_state/ui/crw_web_controller.mm

@@ -2051,9 +2051,11 @@ registerLoadRequestForURL:(const GURL&)requestURL
   }
 
   [self restoreStateFromHistory];
-  // Placeholder navigation is implementation details so should not notify
-  // WebStateObservers.
-  if (!context || !IsPlaceholderUrl(context->GetUrl())) {
+  // Placeholder and restore session URLs are implementation details so should
+  // not notify WebStateObservers.
+  bool isInternalURL = context && (IsPlaceholderUrl(context->GetUrl()) ||
+                                   web::IsRestoreSessionUrl(context->GetUrl()));
+  if (!isInternalURL) {
     _webStateImpl->SetIsLoading(false);
     _webStateImpl->OnPageLoaded(currentURL, loadSuccess);
   }