Fix handling of external protocols with PlzNavigate.

content/common/url_schemes.cc

Index: content/common/url_schemes.cc
diff --git a/content/common/url_schemes.cc b/content/common/url_schemes.cc
index 29a3c85f5bc85c9781189e7e99ef95f611dc5a44..6667cb10b30f9a5bdc657fd0def969345f80a51c 100644
--- a/content/common/url_schemes.cc
+++ b/content/common/url_schemes.cc
@@ -68,6 +68,9 @@ void RegisterContentSchemes(bool lock_schemes) {
   for (auto& scheme : schemes.csp_bypassing_schemes)
     url::AddCSPBypassingScheme(scheme.c_str());
 
+  for (auto& scheme : schemes.empty_document_schemes)
+    url::AddEmptyDocumentScheme(scheme.c_str());
+
   // Prevent future modification of the scheme lists. This is to prevent
   // accidental creation of data races in the program. Add*Scheme aren't
   // threadsafe so must be called when GURL isn't used on any other thread. This