Add media router common classes and unittests.

chrome/browser/media/router/media_route_factory.cc

+// Copyright 2015 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 "chrome/browser/media/router/media_route_factory.h"
+
+#include "base/memory/singleton.h"
+#include "base/strings/string_number_conversions.h"
+#include "chrome/browser/media/router/media_route.h"
+
+namespace media_router {
+namespace {
+const char kRoutePrefix[] = "route-local-";
+}  // namespace
+
+MediaRouteFactory::MediaRouteFactory() : next_id_(0) {}
+
+std::string MediaRouteFactory::NextRouteId() {
+  return kRoutePrefix + base::Uint64ToString(next_id_++);
+}
+
+// static
+MediaRouteFactory* MediaRouteFactory::GetInstance() {
+  return Singleton<MediaRouteFactory>::get();
+}
+
+MediaRoute MediaRouteFactory::Create(const MediaSource& media_source,
+                                     const MediaSinkId& sink_id,
+                                     const std::string& description,
+                                     bool is_local) {
+  DCHECK(CalledOnValidThread());
+  return MediaRoute(NextRouteId(), media_source, sink_id, description,
+                    is_local);
+}
+
+}  // namespace media_router