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

content/renderer/render_frame_impl.cc

Index: content/renderer/render_frame_impl.cc
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
index 301ffe66941c73e077f3ca64cab56286663ed0f2..762dbb1d5facb37574a5db467433747a2523eb34 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -2169,8 +2169,12 @@ void RenderFrameImpl::LoadNavigationErrorPage(
     const WebURLError& error,
     bool replace) {
   std::string error_html;
-  GetContentClient()->renderer()->GetNavigationErrorStrings(
-      this, failed_request, error, &error_html, nullptr);
+
+  if (!RenderThreadImpl::current() ||
+      !RenderThreadImpl::current()->layout_test_mode()) {

[Mike West, 2016/04/25 13:06:21]

It's super-strange that we're checking whether we're in layout test mode here.
Why was the original code doing this check? What tests will fail based on this
change? The world may never know (until the bots come back with results)!

+    GetContentClient()->renderer()->GetNavigationErrorStrings(
+        this, failed_request, error, &error_html, nullptr);
+  }
 
   frame_->loadHTMLString(error_html,
                          GURL(kUnreachableWebDataURL),
@@ -5762,11 +5766,6 @@ bool RenderFrameImpl::ShouldDisplayErrorPageForFailedLoad(
     return false;
   }
 
-  if (RenderThreadImpl::current() &&
-      RenderThreadImpl::current()->layout_test_mode()) {
-    return false;

[Mike West, 2016/04/25 13:06:21]

Returning false here for layout tests means that blink hangs, as nothing ever
loads in the frame, and therefore no `load` event is fired. :(

-  }
-
   return true;
 }