Add CHECK failure to XSRH, to detect which tests exercise this case via a tryjob.

content/browser/loader/cross_site_resource_handler.cc

Index: content/browser/loader/cross_site_resource_handler.cc
diff --git a/content/browser/loader/cross_site_resource_handler.cc b/content/browser/loader/cross_site_resource_handler.cc
index 0b9e6a77aa1f38a0dd34b668a1681bedc5d9fcbe..47c5390f9672fcb57d14e6d3d47fcc0634154a37 100644
--- a/content/browser/loader/cross_site_resource_handler.cc
+++ b/content/browser/loader/cross_site_resource_handler.cc
@@ -96,8 +96,10 @@ CheckNavigationPolicyOnUI(GURL real_url, int process_id, int render_frame_id) {
   // Without a valid RFH against which to check, we must cancel the request,
   // to prevent the resource at |url| from being delivered to a potentially
   // unsuitable renderer process.
-  if (!rfh)
+  if (!rfh) {
+    CHECK(false);
     return CrossSiteResourceHandler::NavigationDecision::CANCEL_REQUEST;
+  }
 
   RenderFrameHostManager* manager = rfh->frame_tree_node()->render_manager();
   if (manager->IsRendererTransferNeededForNavigation(rfh, real_url))