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

chrome/browser/BUILD.gn

Index: chrome/browser/BUILD.gn
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 72df3d62556a394e231a8d2f04a94bd8edf9573e..4f15655f7f58e0d243c6f4d86ba654ec96272131 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -3657,6 +3657,14 @@ split_static_library("browser") {
     deps += [ "//components/payments/content" ]
   }
 
+  if (is_linux || is_win || is_mac) {
+    sources += [
+      "webauth/authenticator_web_contents_manager.cc",
+      "webauth/authenticator_web_contents_manager.h",
+    ]
+    deps += [ "//components/webauth:authenticator" ]
+  }
+
   if (is_linux || is_win) {
     sources += [
       "renderer_context_menu/spelling_options_submenu_observer.cc",