[Nav Experiment] Disable Prerender if WKBasedNavigationManager is used

WKBasedNavigationManager does not yet inject session history into new
WKWebViews created by PrerenderService. Disable PrerenderService for
now so we can measure the load performance impact in Finch experiment.

Bug: 814789
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Iad1db96832dc2e30ab85aa6b8939b8e5850ad250
Reviewed-on: https://chromium-review.googlesource.com/1012494Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Danyao Wang <danyao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551501}

ios/chrome/browser/prerender/prerender_service.mm

@@ -7,6 +7,7 @@
 #import "ios/chrome/browser/prerender/preload_controller.h"
 #import "ios/chrome/browser/tabs/legacy_tab_helper.h"
 #import "ios/chrome/browser/tabs/tab.h"
+#include "ios/web/public/web_client.h"
 #include "ios/web/public/web_state/web_state.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
@@ -32,6 +33,13 @@ void PrerenderService::StartPrerender(const GURL& url,
                                       const web::Referrer& referrer,
                                       ui::PageTransition transition,
                                       bool immediately) {
+  // PrerenderService is not compatible with WKBasedNavigationManager because it
+  // loads the URL in a new WKWebView, which doesn't have the current session
+  // history. TODO(crbug.com/814789): decide whether PrerenderService needs to
+  // be supported after evaluating the performance impact in Finch experiment.
+  if (web::GetWebClient()->IsSlimNavigationManagerEnabled())
+    return;
+
   [controller_ prerenderURL:url
                    referrer:referrer
                  transition:transition