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..9c28def41f6067418564129f489844252f5b2830 100644
--- a/content/browser/loader/navigation_resource_throttle.cc
+++ b/content/browser/loader/navigation_resource_throttle.cc
@@ -235,6 +235,15 @@ void NavigationResourceThrottle::OnUIChecksPerformed(
     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();
   }