[ios] Purge web view if external app URL is current in navigation stack.

ios/web/web_state/ui/crw_web_controller.mm

 // Copyright 2012 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_web_controller.h"
 
 #import <WebKit/WebKit.h>
 
 #import <objc/runtime.h>
 #include <stddef.h>
@@ skipping 3325 matching lines @@
   // application? For example, only allow it for TYPED and LINK transitions.
   if (![CRWWebController webControllerCanShow:requestURL]) {
     if (![self shouldOpenExternalURLForNavigationAction:action]) {
       return NO;
     }
 
     // Stop load if navigation is believed to be happening on the main frame.
     if ([self isMainFrameNavigationAction:action])
       [self stopLoading];
 
+    // Purge web view if last committed URL is different from the document URL.
+    // This can happen if external URL was added to the navigation stack and was
+    // loaded using Go Back or Go Forward navigation (in which case document URL
+    // will point to the previous page).
+    GURL lastCommittedURL =
+        self.webState->GetNavigationManager()->GetLastCommittedItem()->GetURL();
+    if (lastCommittedURL != _documentURL) {
+      [self requirePageReconstruction];
+      [self setDocumentURL:lastCommittedURL];
+    }
+
     if ([_delegate openExternalURL:requestURL
                        linkClicked:isNavigationTypeLinkActivated]) {
       // Record the URL so that errors reported following the 'NO' reply can be
       // safely ignored.
       [_openedApplicationURL addObject:request.URL];
       if ([self shouldClosePageOnNativeApplicationLoad])
         [_delegate webPageOrderedClose];
     }
     return NO;
   }
@@ skipping 2278 matching lines @@
   }
 
   return web::WEB_VIEW_DOCUMENT_TYPE_GENERIC;
 }
 
 - (NSString*)refererFromNavigationAction:(WKNavigationAction*)action {
   return [action.request valueForHTTPHeaderField:@"Referer"];
 }
 
 @end