(Re-)introduce AncestorThrottle to handle 'X-Frame-Options'.

content/browser/loader/navigation_resource_throttle.cc

 // Copyright 2015 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.
 
 #include "content/browser/loader/navigation_resource_throttle.h"
 
 #include <memory>
 
 #include "base/bind.h"
 #include "base/callback.h"
@@ skipping 327 matching lines @@
     on_transfer_done_result_ = result;
     return;
   }
 
   if (result == NavigationThrottle::CANCEL_AND_IGNORE) {
     CancelAndIgnore();
   } else if (result == NavigationThrottle::CANCEL) {
     Cancel();
   } else if (result == NavigationThrottle::BLOCK_REQUEST) {
     CancelWithError(net::ERR_BLOCKED_BY_CLIENT);
+  } else if (result == NavigationThrottle::BLOCK_RESPONSE) {
+    // TODO(mkwst): If we cancel the main frame request with anything other than
+    // 'net::ERR_ABORTED', we'll trigger some special behavior that might not be
+    // desirable here (non-POSTs will reload the page, while POST has some logic
+    // around reloading to avoid duplicating actions server-side). For the
+    // moment, only child frame navigations should be blocked. If we need to
+    // block main frame navigations in the future, we'll need to carefully
+    // consider the right thing to do here.
+    DCHECK(!ResourceRequestInfo::ForRequest(request_)->IsMainFrame());
+    CancelWithError(net::ERR_BLOCKED_BY_RESPONSE);
   } else {
     Resume();
   }
 }
 
 void NavigationResourceThrottle::InitiateTransfer() {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   in_cross_site_transition_ = true;
   ResourceRequestInfoImpl* info =
       ResourceRequestInfoImpl::ForRequest(request_);
@@ skipping 10 matching lines @@
 
   // If the results of the checks on the UI thread are known, unblock the
   // navigation. Otherwise, wait until the callback has executed.
   if (on_transfer_done_result_ != NavigationThrottle::DEFER) {
     OnUIChecksPerformed(on_transfer_done_result_);
     on_transfer_done_result_ = NavigationThrottle::DEFER;
   }
 }
 
 }  // namespace content