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 bd7a5864dc2b65837835d67eaeb75cd9d5ae1532..e4006938de27c8c705e5953b36babf35ab7e2a28 100644
--- a/content/child/runtime_features.cc
+++ b/content/child/runtime_features.cc
@@ -391,6 +391,10 @@ void SetRuntimeFeaturesDefaultsAndUpdateFromArgs(
   WebRuntimeFeatures::EnableLocationHardReload(
       base::FeatureList::IsEnabled(features::kLocationHardReload));
 
+  if (!base::FeatureList::IsEnabled(features::kWebAuth) &&
+      !enableExperimentalWebPlatformFeatures)
+    WebRuntimeFeatures::EnableWebAuth(false);
+
   // Enable explicitly enabled features, and then disable explicitly disabled
   // ones.
   if (command_line.HasSwitch(switches::kEnableBlinkFeatures)) {