[Media Router] Connection state change listening redesign part 2.

chrome/browser/media/router/media_router_base.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_router_base.h"
+
+#include "base/bind.h"
+
+namespace media_router {
+
+MediaRouterBase::MediaRouterBase() = default;
+
+MediaRouterBase::~MediaRouterBase() = default;
+
+scoped_ptr<PresentationConnectionStateSubscription>
+MediaRouterBase::AddPresentationConnectionStateChangedCallback(
+    const MediaRoute::Id& route_id,
+    const content::PresentationConnectionStateChangedCallback& callback) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  auto* callbacks = presentation_connection_state_callbacks_.get(route_id);
+  if (!callbacks) {
+    callbacks = new PresentationConnectionStateChangedCallbacks;
+    callbacks->set_removal_callback(base::Bind(
+        &MediaRouterBase::OnPresentationConnectionStateCallbackRemoved,
+        base::Unretained(this), route_id));
+    presentation_connection_state_callbacks_.add(route_id,
+                                                 make_scoped_ptr(callbacks));
+  }
+
+  return callbacks->Add(callback);
+}
+
+void MediaRouterBase::NotifyPresentationConnectionStateChange(
+    const MediaRoute::Id& route_id,
+    content::PresentationConnectionState state) {
+  auto* callbacks = presentation_connection_state_callbacks_.get(route_id);
+  if (!callbacks)
+    return;
+
+  callbacks->Notify(state);
+}
+
+void MediaRouterBase::OnPresentationConnectionStateCallbackRemoved(
+    const MediaRoute::Id& route_id) {
+  auto* callbacks = presentation_connection_state_callbacks_.get(route_id);
+  if (callbacks && callbacks->empty())
+    presentation_connection_state_callbacks_.erase(route_id);
+}
+
+}  // namespace media_router