[Media Router] Add P1 UMA metrics for Media Router.

chrome/browser/media/router/media_router_metrics.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_metrics.h"
+
+#include "base/metrics/histogram_macros.h"
+
+namespace media_router {
+
+// static
+void MediaRouterMetrics::RecordMediaRouterDialogOrigin(
+    MediaRouterDialogOpenOrigin origin) {
+  UMA_HISTOGRAM_ENUMERATION("MediaRouter.Icon.Click.Location",
+                            origin, media_router::TOTAL_COUNT);
+}
+
+}  // namespace media_router