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

content/public/browser/navigation_throttle.h

 // 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.
 
 #ifndef CONTENT_PUBLIC_BROWSER_NAVIGATION_THROTTLE_H_
 #define CONTENT_PUBLIC_BROWSER_NAVIGATION_THROTTLE_H_
 
 #include "content/common/content_export.h"
 
 namespace content {
@@ skipping 14 matching lines @@
     // If the NavigationHandle is destroyed while the navigation is deferred,
     // the navigation will be canceled in the network stack.
     DEFER,
 
     // Cancels the navigation.
     CANCEL,
 
     // Cancels the navigation and makes the requester of the navigation acts
     // like the request was never made.
     CANCEL_AND_IGNORE,
+
+    // Blocks a navigation due to rules asserted by a response (for instance,
+    // embedding restrictions like 'X-Frame-Options'). This result will only
+    // be returned from WillProcessResponse.

[carlosk, 2016/05/10 14:05:36]

Should also mention that BLOCK_RESPONSE should only be used for subframes (for
now at least, as stated in navigation_resource_throttle.cc).

+    BLOCK_RESPONSE,
   };
 
   NavigationThrottle(NavigationHandle* navigation_handle);
   virtual ~NavigationThrottle();
 
   // Called when a network request is about to be made for this navigation.
   //
   // The implementer is responsible for ensuring that the WebContents this
   // throttle is associated with remain alive during the duration of this
   // method. Failing to do so will result in use-after-free bugs. Should the
   // implementer need to destroy the WebContents, it should return CANCEL,
   // CANCEL_AND_IGNORE or DEFER and perform the destruction asynchronously.
   virtual ThrottleCheckResult WillStartRequest();
 
   // Called when a server redirect is received by the navigation.
   //
   // The implementer is responsible for ensuring that the WebContents this
   // throttle is associated with remain alive during the duration of this
   // method. Failing to do so will result in use-after-free bugs. Should the
   // implementer need to destroy the WebContents, it should return CANCEL,
   // CANCEL_AND_IGNORE or DEFER and perform the destruction asynchronously.
   virtual ThrottleCheckResult WillRedirectRequest();
 
   // Called when a response's headers and metadata are available.
   //
   // The implementer is responsible for ensuring that the WebContents this
   // throttle is associated with remain alive during the duration of this
   // method. Failing to do so will result in use-after-free bugs. Should the
   // implementer need to destroy the WebContents, it should return CANCEL,
-  // CANCEL_AND_IGNORE and perform the destruction asynchronously.
+  // CANCEL_AND_IGNORE, or BLOCK_RESPONSE and perform the destruction
+  // asynchronously.
   virtual ThrottleCheckResult WillProcessResponse();
 
   // The NavigationHandle that is tracking the information related to this
   // navigation.
   NavigationHandle* navigation_handle() const { return navigation_handle_; }
 
  private:
   NavigationHandle* navigation_handle_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_NAVIGATION_THROTTLE_H_