Use a resource throttle to implement shouldOverrideUrlLoading.

content/child/web_url_request_util.cc

Index: content/child/web_url_request_util.cc
diff --git a/content/child/web_url_request_util.cc b/content/child/web_url_request_util.cc
index 6737307c744b5af3a2d255c3d3a82234da880c55..19d7b5af7fcc7285a43d905be2b9e9b648e3fa11 100644
--- a/content/child/web_url_request_util.cc
+++ b/content/child/web_url_request_util.cc
@@ -299,4 +299,14 @@ blink::WebURLError CreateWebURLError(const blink::WebURL& unreachable_url,
   return error;
 }
 
+blink::WebURLError CreateWebURLError(const blink::WebURL& unreachable_url,
+                                     bool stale_copy_in_cache,
+                                     int reason,
+                                     bool was_ignored_by_handler) {
+  blink::WebURLError error =
+      CreateWebURLError(unreachable_url, stale_copy_in_cache, reason);
+  error.wasIgnoredByHandler = was_ignored_by_handler;
+  return error;
+}
+
 }  // namespace content