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

content/browser/frame_host/navigation_handle_impl.cc

Index: content/browser/frame_host/navigation_handle_impl.cc
diff --git a/content/browser/frame_host/navigation_handle_impl.cc b/content/browser/frame_host/navigation_handle_impl.cc
index de17b3247fe2833c2391349fcde9bb32c57d688e..b9a646ef300003fc0564027d4e3b9974532ec6af 100644
--- a/content/browser/frame_host/navigation_handle_impl.cc
+++ b/content/browser/frame_host/navigation_handle_impl.cc
@@ -6,6 +6,7 @@
 
 #include <utility>
 
+#include "content/browser/frame_host/ancestor_throttle.h"
 #include "content/browser/frame_host/frame_tree_node.h"
 #include "content/browser/frame_host/navigator.h"
 #include "content/browser/frame_host/navigator_delegate.h"
@@ -233,10 +234,13 @@ void NavigationHandleImpl::WillStartRequest(
   state_ = WILL_SEND_REQUEST;
   complete_callback_ = callback;
 
-  // Register the navigation throttles. The ScopedVector returned by
-  // GetNavigationThrottles is not assigned to throttles_ directly because it
-  // would overwrite any throttle previously added with
-  // RegisterThrottleForTesting.
+  // Register the platform's navigation throttles.
+  scoped_ptr<content::NavigationThrottle> ancestor_throttle =
+      AncestorThrottle::MaybeCreateThrottleFor(this);
+  if (ancestor_throttle)
+    throttles_.push_back(std::move(ancestor_throttle));
+
+  // Register the embedder's navigation throttles.
   ScopedVector<NavigationThrottle> throttles_to_register =
       GetContentClient()->browser()->CreateThrottlesForNavigation(this);
   if (throttles_to_register.size() > 0) {
@@ -343,7 +347,7 @@ NavigationHandleImpl::CheckWillStartRequest() {
         next_index_ = i + 1;
         return result;
 
-      default:
+      case NavigationThrottle::BLOCK_RESPONSE:

[nasko, 2016/02/12 23:21:40]

Why did we lose the default?

[Mike West, 2016/04/12 20:13:30]

Because this completely enumerates all the options of
`NavigationThrottle::ThrottleCheckResult`, so the `default:` will never be hit,
and the compiler will tell us when we need to add a new item?

         NOTREACHED();
     }
   }
@@ -374,7 +378,7 @@ NavigationHandleImpl::CheckWillRedirectRequest() {
         next_index_ = i + 1;
         return result;
 
-      default:
+      case NavigationThrottle::BLOCK_RESPONSE:
         NOTREACHED();
     }
   }
@@ -393,6 +397,7 @@ NavigationHandleImpl::CheckWillProcessResponse() {
       case NavigationThrottle::PROCEED:
         continue;
 
+      case NavigationThrottle::BLOCK_RESPONSE:
       case NavigationThrottle::CANCEL:
       case NavigationThrottle::CANCEL_AND_IGNORE:
         state_ = CANCELING;