Add a Physical Web data source

components/physical_web_data_source/physical_web_data_source.cc

+// Copyright 2016 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.
+
+#include "components/physical_web_data_source/physical_web_data_source.h"
+
+namespace {
+PhysicalWebDataSource* g_physical_web_data_source = nullptr;
+}
+
+PhysicalWebDataSource::PhysicalWebDataSource() {}
+
+PhysicalWebDataSource::~PhysicalWebDataSource() {}
+
+// static
+PhysicalWebDataSource* PhysicalWebDataSource::GetInstance() {
+  return g_physical_web_data_source;
+}
+
+// static
+void PhysicalWebDataSource::SetInstance(
+    PhysicalWebDataSource* instance) {
+  g_physical_web_data_source = instance;
+}