Implement Ukm Mojo interface.

components/ukm/public/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")
 
 static_library("public") {
   sources = [
+    "mojo_ukm_recorder.cc",
+    "mojo_ukm_recorder.h",
     "ukm_entry_builder.cc",
     "ukm_entry_builder.h",
     "ukm_recorder.cc",
     "ukm_recorder.h",
   ]
 
   public_deps = [
     "//base",
     "//components/ukm/public/interfaces",
     "//url",
   ]
 
   deps = [
     "//mojo/public/cpp/bindings",
   ]
 }