Fixing WKWebView QuickBack

ios/web/web_state/ui/crw_wk_web_view_web_controller.mm

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/web/web_state/ui/crw_wk_web_view_web_controller.h"
 
 #import <WebKit/WebKit.h>
 
 #include "base/ios/ios_util.h"
 #include "base/ios/weak_nsobject.h"
@@ skipping 431 matching lines @@
 - (void)loadRequestForCurrentNavigationItem {
   DCHECK(self.webView && !self.nativeController);
 
   ProceduralBlock defaultNavigationBlock = ^{
     [self registerLoadRequest:[self currentNavigationURL]
                      referrer:[self currentSessionEntryReferrer]
                    transition:[self currentTransition]];
     [self loadRequest:[self requestForCurrentNavigationItem]];
   };
 
-  // If there is no corresponding WKBackForwardListItem, fall back to
-  // the standard loading mechanism.
+  // If there is no corresponding WKBackForwardListItem, or the item is not in
+  // the current WKWebView's back-forward list, navigating using WKWebView API
+  // is not possible. In this case, fall back to the default navigation
+  // mechanism.
   web::WKBackForwardListItemHolder* holder =
       [self currentBackForwardListItemHolder];
-  if (!holder->back_forward_list_item()) {
+  if (!holder->back_forward_list_item() ||
+      ![self isBackForwardListItemValid:holder->back_forward_list_item()]) {
     defaultNavigationBlock();
     return;
   }
 
-  // The current back-forward list item MUST be in the WKWebView's back-forward
-  // list to be valid.
-  DCHECK([self isBackForwardListItemValid:holder->back_forward_list_item()]);
-
   ProceduralBlock webViewNavigationBlock = ^{
     // If the current navigation URL is the same as the URL of the visible
     // page, that means the user requested a reload. |goToBackForwardListItem|
     // will be a no-op when it is passed the current back forward list item,
     // so |reload| must be explicitly called.
     [self registerLoadRequest:[self currentNavigationURL]
                      referrer:[self currentSessionEntryReferrer]
                    transition:[self currentTransition]];
     if ([self currentNavigationURL] == net::GURLWithNSURL([_wkWebView URL])) {
       [_wkWebView reload];
@@ skipping 943 matching lines @@
                               placeholderText:defaultText
                                    requestURL:
             net::GURLWithNSURL(frame.request.URL)
                             completionHandler:completionHandler];
   } else if (completionHandler) {
     completionHandler(nil);
   }
 }
 
 @end