Reland "[ios] Enable preload with slim-navigation-manager."

This reverts commit ceff1a21.

Reason for revert: Fixed.

Original change's description:
> Revert "[ios] Enable preload with slim-navigation-manager."
>
> This reverts commit 101b5ae0.
>
> Reason for revert: Needs some more work, some last minute
> refactoring introduced some crashes.
>
> Original change's description:
> > [ios] Enable preload with slim-navigation-manager.
> >
> > Previously, preload required CopyStateFromAndPrune and
> > CanPruneAllButLastCommittedItem within NavigationManager, but those
> > are not supported with SlimNav. Here, preload is implemented by
> > creating a preload WebState with navigation history by restoring the
> > current WebState.
> >
> > The performance of this implementation depends on Slim
> > Navigation Manager's session restoration performance which can be
> > measured with existing kRestoreNavigationTime metric.
> >
> > Original implementation of this CL was written by eugenebut@,
> > simply updated in this resurrected CL.
> >
> > Bug: 834116
> > Change-Id: I86c9ecf7e3ed213ebaeddce6264dff3bbb8a8c94
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1815702
> > Commit-Queue: Justin Cohen <justincohen@chromium.org>
> > Reviewed-by: Rohit Rao <rohitrao@chromium.org>
> > Reviewed-by: Eugene But <eugenebut@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#701228}
>
> TBR=rohitrao@chromium.org,justincohen@chromium.org,eugenebut@chromium.org,gambard@chromium.org
>
> # Not skipping CQ checks because original CL landed > 1 day ago.
>
> Bug: 834116
> Change-Id: I16beb96bc2d1eab9a9c36a8e03728fd3cc23f035
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1833743
> Reviewed-by: Justin Cohen <justincohen@chromium.org>
> Commit-Queue: Justin Cohen <justincohen@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#701746}

Change-Id: I52889208ed3a84c08c66742e72b524adce0560af
Bug: 834116
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1833706Reviewed-by: Eugene But <eugenebut@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Auto-Submit: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#702004}

ios/chrome/browser/prerender/preload_controller.mm

@@ -32,6 +32,7 @@
 #import "ios/web/public/navigation/web_state_policy_decider_bridge.h"
 #include "ios/web/public/thread/web_thread.h"
 #import "ios/web/public/ui/java_script_dialog_presenter.h"
+#include "ios/web/public/web_client.h"
 #import "ios/web/public/web_state.h"
 #import "ios/web/public/web_state_observer_bridge.h"
 #import "ios/web/web_state/ui/crw_web_controller.h"
@@ -322,7 +323,8 @@ class PreloadJavaScriptDialogPresenter : public web::JavaScriptDialogPresenter {
 }
 
 - (std::unique_ptr<web::WebState>)releasePrerenderContents {
-  if (!_webState)
+  if (!_webState ||
+      _webState->GetNavigationManager()->IsRestoreSessionInProgress())
     return nullptr;
 
   self.successfulPrerendersPerSessionCount++;
@@ -495,13 +497,20 @@ class PreloadJavaScriptDialogPresenter : public web::JavaScriptDialogPresenter {
   self.prerenderedURL = self.scheduledURL;
   std::unique_ptr<PrerenderRequest> request = std::move(_scheduledRequest);
 
-  if (!self.prerenderedURL.is_valid()) {
+  web::WebState* webStateToReplace = [self.delegate webStateToReplace];
+  if (!self.prerenderedURL.is_valid() || !webStateToReplace) {
     [self destroyPreviewContents];
     return;
   }
 
   web::WebState::CreateParams createParams(self.browserState);
-  _webState = web::WebState::Create(createParams);
+  if (web::GetWebClient()->IsSlimNavigationManagerEnabled()) {
+    _webState = web::WebState::CreateWithStorageSession(
+        createParams, webStateToReplace->BuildSessionStorage());
+  } else {
+    _webState = web::WebState::Create(createParams);
+  }
+
   // Add the preload controller as a policyDecider before other tab helpers, so
   // that it can block the navigation if needed before other policy deciders
   // execute thier side effects (eg. AppLauncherTabHelper launching app).

ios/chrome/browser/prerender/preload_controller_delegate.h

@@ -12,6 +12,10 @@
 // A protocol implemented by a delegate of PreloadController
 @protocol PreloadControllerDelegate
 
+// WebState from which preload controller should copy the session history.
+// This web state will be replaced on successful preload.
+- (web::WebState*)webStateToReplace;
+
 // Should preload controller request a desktop site.
 - (BOOL)preloadShouldUseDesktopUserAgent;
 

ios/chrome/browser/prerender/prerender_egtest.mm

@@ -65,11 +65,6 @@ std::unique_ptr<net::test_server::HttpResponse> StandardResponse(
         @"Disabled for iPad due to alternate letters educational screen.");
   }
 
-  if ([ChromeEarlGrey isSlimNavigationManagerEnabled]) {
-    // TODO(crbug.com/834116): Fix and enable this test.
-    EARL_GREY_TEST_DISABLED(@"Prerender is not supported by slim-nav yet.");
-  }
-
   [ChromeEarlGrey clearBrowsingHistory];
   // Set server up.
   int visitCounter = 0;

ios/chrome/browser/prerender/prerender_service.mm

@@ -39,13 +39,6 @@ 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
@@ -64,6 +57,11 @@ bool PrerenderService::MaybeLoadPrerenderedURL(
 
   std::unique_ptr<web::WebState> new_web_state =
       [controller_ releasePrerenderContents];
+  if (!new_web_state) {
+    CancelPrerender();
+    return false;
+  }
+
   DCHECK_NE(WebStateList::kInvalidIndex, web_state_list->active_index());
 
   web::NavigationManager* active_navigation_manager =
@@ -79,8 +77,13 @@ bool PrerenderService::MaybeLoadPrerenderedURL(
   web::NavigationManager* new_navigation_manager =
       new_web_state->GetNavigationManager();
 
-  if (new_navigation_manager->CanPruneAllButLastCommittedItem()) {
-    new_navigation_manager->CopyStateFromAndPrune(active_navigation_manager);
+  bool slim_navigation_manager_enabled =
+      web::GetWebClient()->IsSlimNavigationManagerEnabled();
+  if (new_navigation_manager->CanPruneAllButLastCommittedItem() ||
+      slim_navigation_manager_enabled) {
+    if (!slim_navigation_manager_enabled) {
+      new_navigation_manager->CopyStateFromAndPrune(active_navigation_manager);
+    }
     loading_prerender_ = true;
     web_state_list->ReplaceWebStateAt(web_state_list->active_index(),
                                       std::move(new_web_state));

ios/chrome/browser/ui/browser_view/browser_view_controller.mm

@@ -4757,6 +4757,10 @@ NSString* const kBrowserViewControllerSnackbarCategory =
   return [self userAgentType] == web::UserAgentType::DESKTOP;
 }
 
+- (web::WebState*)webStateToReplace {
+  return self.currentWebState;
+}
+
 #pragma mark - NetExportTabHelperDelegate
 
 - (void)netExportTabHelper:(NetExportTabHelper*)tabHelper