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/+/1833743Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701746}

ios/chrome/browser/prerender/preload_controller.h

@@ -71,11 +71,10 @@ class WebState;
 // Returns whether |webState| is the WebState used for pre-rendering.
 - (BOOL)isWebStatePrerendered:(web::WebState*)webState;
 
-// Returns the currently prerendered WebState, or nil if it was not created
-// while |oldWebState| was active, or nil if none exists.  After this method is
-// called, the PrerenderController reverts to a non-prerendering state.
-- (std::unique_ptr<web::WebState>)releasePrerenderContentsForWebState:
-    (web::WebState*)oldWebState;
+// Returns the currently prerendered WebState, or nil if none exists.  After
+// this method is called, the PrerenderController reverts to a non-prerendering
+// state.
+- (std::unique_ptr<web::WebState>)releasePrerenderContents;
 
 @end
 

ios/chrome/browser/prerender/preload_controller.mm

@@ -32,7 +32,6 @@
 #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"
@@ -187,10 +186,6 @@ class PreloadJavaScriptDialogPresenter : public web::JavaScriptDialogPresenter {
 // there is no prerender scheduled.
 @property(nonatomic, readonly) const GURL& scheduledURL;
 
-// Contains the original webState that, for SlimNav, session history will be
-// created from.
-@property(nonatomic, assign) web::WebState* webStateToReplace;
-
 // Whether or not the preference is enabled.
 @property(nonatomic, getter=isPreferenceEnabled) BOOL preferenceEnabled;
 
@@ -304,9 +299,6 @@ class PreloadJavaScriptDialogPresenter : public web::JavaScriptDialogPresenter {
   }
 
   [self removeScheduledPrerenderRequests];
-
-  self.webStateToReplace = [self.delegate webStateToReplace];
-
   _scheduledRequest =
       std::make_unique<PrerenderRequest>(url, transition, referrer);
 
@@ -329,13 +321,10 @@ class PreloadJavaScriptDialogPresenter : public web::JavaScriptDialogPresenter {
   return webState && _webState.get() == webState;
 }
 
-- (std::unique_ptr<web::WebState>)releasePrerenderContentsForWebState:
-    (web::WebState*)oldWebState {
-  if (!_webState || oldWebState != self.webStateToReplace ||
-      _webState->GetNavigationManager()->IsRestoreSessionInProgress())
+- (std::unique_ptr<web::WebState>)releasePrerenderContents {
+  if (!_webState)
     return nullptr;
 
-  self.webStateToReplace = nullptr;
   self.successfulPrerendersPerSessionCount++;
   [self recordReleaseMetrics];
   [self removeScheduledPrerenderRequests];
@@ -512,13 +501,7 @@ class PreloadJavaScriptDialogPresenter : public web::JavaScriptDialogPresenter {
   }
 
   web::WebState::CreateParams createParams(self.browserState);
-  if (web::GetWebClient()->IsSlimNavigationManagerEnabled()) {
-    _webState = web::WebState::CreateWithStorageSession(
-        createParams, self.webStateToReplace->BuildSessionStorage());
-  } else {
-    _webState = web::WebState::Create(createParams);
-  }
-
+  _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).
@@ -580,7 +563,6 @@ class PreloadJavaScriptDialogPresenter : public web::JavaScriptDialogPresenter {
 
   self.prerenderedURL = GURL();
   self.startTime = base::TimeTicks();
-  self.webStateToReplace = nullptr;
 }
 
 #pragma mark - Notification Helpers

ios/chrome/browser/prerender/preload_controller_delegate.h

@@ -12,10 +12,6 @@
 // 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/preload_controller_unittest.mm

@@ -116,7 +116,7 @@ TEST_F(PreloadControllerTest, DontPreloadNonWebURLs) {
                    referrer:kReferrer
                  transition:kTransition
                 immediately:YES];
-  EXPECT_FALSE([controller_ releasePrerenderContentsForWebState:nil]);
+  EXPECT_FALSE([controller_ releasePrerenderContents]);
 
   // Attempt to prerender the NTP and verify that no WebState was created
   // to preload.
@@ -124,7 +124,7 @@ TEST_F(PreloadControllerTest, DontPreloadNonWebURLs) {
                    referrer:kReferrer
                  transition:kTransition
                 immediately:YES];
-  EXPECT_FALSE([controller_ releasePrerenderContentsForWebState:nil]);
+  EXPECT_FALSE([controller_ releasePrerenderContents]);
 
   // Attempt to prerender the flags UI and verify that no WebState was created
   // to preload.
@@ -132,7 +132,7 @@ TEST_F(PreloadControllerTest, DontPreloadNonWebURLs) {
                    referrer:kReferrer
                  transition:kTransition
                 immediately:YES];
-  EXPECT_FALSE([controller_ releasePrerenderContentsForWebState:nil]);
+  EXPECT_FALSE([controller_ releasePrerenderContents]);
 }
 
 TEST_F(PreloadControllerTest, TestIsPrerenderingEnabled_preloadAlways) {

ios/chrome/browser/prerender/prerender_egtest.mm

@@ -65,6 +65,11 @@ 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

@@ -39,6 +39,13 @@ 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
@@ -55,18 +62,12 @@ bool PrerenderService::MaybeLoadPrerenderedURL(
     return false;
   }
 
-  web::WebState* web_state = web_state_list->GetActiveWebState();
   std::unique_ptr<web::WebState> new_web_state =
-      [controller_ releasePrerenderContentsForWebState:web_state];
-  if (!new_web_state) {
-    CancelPrerender();
-    return false;
-  }
-
+      [controller_ releasePrerenderContents];
   DCHECK_NE(WebStateList::kInvalidIndex, web_state_list->active_index());
 
   web::NavigationManager* active_navigation_manager =
-      web_state->GetNavigationManager();
+      web_state_list->GetActiveWebState()->GetNavigationManager();
   int lastIndex = active_navigation_manager->GetLastCommittedItemIndex();
   UMA_HISTOGRAM_COUNTS_100("Prerender.PrerenderLoadedOnIndex", lastIndex);
 
@@ -78,13 +79,8 @@ bool PrerenderService::MaybeLoadPrerenderedURL(
   web::NavigationManager* new_navigation_manager =
       new_web_state->GetNavigationManager();
 
-  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);
-    }
+  if (new_navigation_manager->CanPruneAllButLastCommittedItem()) {
+    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

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