Add the Mojo implementation of authenticator.mojom's MakeCredential.

content/child/runtime_features.cc

Index: content/child/runtime_features.cc
diff --git a/content/child/runtime_features.cc b/content/child/runtime_features.cc
index a240fa224fe939f75364c518752e233ebc7ec6ad..263521fd58204d2647d36008f1b9c07864a7dfd3 100644
--- a/content/child/runtime_features.cc
+++ b/content/child/runtime_features.cc
@@ -379,6 +379,9 @@ void SetRuntimeFeaturesDefaultsAndUpdateFromArgs(
   WebRuntimeFeatures::EnableLocationHardReload(
       base::FeatureList::IsEnabled(features::kLocationHardReload));
 
+  if (!base::FeatureList::IsEnabled(features::kWebAuth))
+    WebRuntimeFeatures::EnableWebAuth(false);
+
   // Enable explicitly enabled features, and then disable explicitly disabled
   // ones.
   if (command_line.HasSwitch(switches::kEnableBlinkFeatures)) {