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 d8c840e29a8801482226fc08ac751317ddee32ca..2df15a4791ea756a1d27bcf58dc811df0086b6b7 100644
--- a/content/child/runtime_features.cc
+++ b/content/child/runtime_features.cc
@@ -375,6 +375,9 @@ void SetRuntimeFeaturesDefaultsAndUpdateFromArgs(
                                                 false);
   }
 
+  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)) {