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

content/browser/loader/navigation_resource_throttle.cc

Index: content/browser/loader/navigation_resource_throttle.cc
diff --git a/content/browser/loader/navigation_resource_throttle.cc b/content/browser/loader/navigation_resource_throttle.cc
index 9112f7e8d8919dba6030a0eeae48843563e48c21..1a9b3fa634fffe6f898fb2a4509702e6e58dd150 100644
--- a/content/browser/loader/navigation_resource_throttle.cc
+++ b/content/browser/loader/navigation_resource_throttle.cc
@@ -235,6 +235,10 @@ void NavigationResourceThrottle::OnUIChecksPerformed(
     controller()->CancelAndIgnore();
   } else if (result == NavigationThrottle::CANCEL) {
     controller()->Cancel();
+  } else if (result == NavigationThrottle::BLOCK_RESPONSE) {
+    // TODO(mkwst): Replace this with something more specific, as the error
+    // page for this code is meant for use with extensions.
+    controller()->CancelWithError(net::ERR_BLOCKED_BY_CLIENT);
   } else {
     controller()->Resume();
   }