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

components/webauth/BUILD.gn

 # Copyright 2017 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//mojo/public/tools/bindings/mojom.gni")
 
-mojom("authenticator") {
+source_set("authenticator") {
   sources = [
-    "authenticator.mojom",
+    "authenticator_impl.cc",
+    "authenticator_impl.h",
   ]
 
-  public_deps = [
-    "//mojo/common:common_custom_types",
+  deps = [
+    "//base",
+    "//content/public/browser",
+    "//mojo/common",
+    "//mojo/public/cpp/bindings",
+    "//third_party/WebKit/public:blink_headers",
   ]
 }
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "authenticator_impl_unittest.cc",
+  ]
+  deps = [
+    "//base/test:test_support",
+    "//content/test:test_support",
+    "//mojo/common",
+    "//mojo/public/cpp/bindings",
+    "//testing/gmock",
+    "//testing/gtest",
+    "//third_party/WebKit/public:blink_headers",
+  ]
+}