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

components/webauth/BUILD.gn

Index: components/webauth/BUILD.gn
diff --git a/components/webauth/BUILD.gn b/components/webauth/BUILD.gn
index 80da9afb1b310f04d338c8860971810f173bcacf..e8995feaef7cedc3688a9984b2b29d3e7abe7040 100644
--- a/components/webauth/BUILD.gn
+++ b/components/webauth/BUILD.gn
@@ -4,12 +4,37 @@
 
 import("//mojo/public/tools/bindings/mojom.gni")
 
-mojom("authenticator") {
+source_set("authenticator") {
   sources = [
-    "authenticator.mojom",
+    "authenticator_impl.cc",
+    "authenticator_impl.h",
+    "authenticator_web_contents_manager.cc",
+    "authenticator_web_contents_manager.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",
+    "authenticator_web_contents_manager_unittest.cc",
+  ]
+  deps = [
+    ":authenticator",
+    "//base/test:test_support",
+    "//content/test:test_support",
+    "//mojo/common",
+    "//mojo/public/cpp/bindings",
+    "//testing/gmock",
+    "//testing/gtest",
+    "//third_party/WebKit/public:blink_headers",
   ]
 }