Introduce AncestorThrottle, which will process 'X-Frame-Options' headers.

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 "base/bind.h"
 #include "base/callback.h"
 #include "base/location.h"
 #include "base/logging.h"
@@ skipping 217 matching lines @@
   return "NavigationResourceThrottle";
 }
 
 void NavigationResourceThrottle::OnUIChecksPerformed(
     NavigationThrottle::ThrottleCheckResult result) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   if (result == NavigationThrottle::CANCEL_AND_IGNORE) {
     controller()->CancelAndIgnore();
   } else if (result == NavigationThrottle::CANCEL) {
     controller()->Cancel();
+  } 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.

[mmenke, 2016/05/05 12:36:27]

Can we add a DCHECK here, too (Grab the ResourceRequestInfo::ForRequest, and
DCHECK it's not a main frame), just to make sure if that changes, someone thinks
about the issue?

+    controller()->CancelWithError(net::ERR_BLOCKED_BY_RESPONSE);
   } else {
     controller()->Resume();
   }
 }
 
 }  // namespace content