[ios] Do not allow loading chrome:// URLs from regular http/https pages.

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"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 1415 matching lines @@
   // lastRegisteredRequestURL may be the same as the webViewURL on a new tab
   // created by window.open (default is about::blank).
   if (self.lastRegisteredRequestURL != webViewURL ||
       self.loadPhase != web::LOAD_REQUESTED) {
     // Reset current WebUI if one exists.
     [self clearWebUI];
     // Restart app specific URL loads to properly capture state.
     // TODO(crbug.com/546347): Extract necessary tasks for app specific URL
     // navigation rather than restarting the load.
     if (web::GetWebClient()->IsAppSpecificURL(webViewURL)) {
-      [self abortWebLoad];
-      NavigationManager::WebLoadParams params(webViewURL);
-      [self loadWithParams:params];
+      // Renderer-initiated loads of WebUI can be done only from other WebUI
+      // pages. WebUI pages may have increased power and using the same web
+      // process (which may potentially be controller by an attacker) is
+      // dangerous.
+      if (web::GetWebClient()->IsAppSpecificURL(_documentURL)) {
+        [self abortWebLoad];
+        NavigationManager::WebLoadParams params(webViewURL);
+        [self loadWithParams:params];
+      }
       return;
     } else {
       [self registerLoadRequest:webViewURL];
     }
   }
   // Ensure the URL is registered and loadPhase is as expected.
   DCHECK(self.lastRegisteredRequestURL == webViewURL);
   DCHECK(self.loadPhase == web::LOAD_REQUESTED);
   _latestWKNavigation.reset([navigation retain]);
 }
@@ skipping 273 matching lines @@
         runJavaScriptTextInputPanelWithPrompt:prompt
                                   defaultText:defaultText
                                    requestURL:requestURL
                             completionHandler:completionHandler];
   } else if (completionHandler) {
     completionHandler(nil);
   }
 }
 
 @end