Make MediaSession a runtime-enabled feature on Desktop.

content/browser/media/session/media_session_delegate_default_browsertest.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 "base/command_line.h"
+#include "content/browser/media/session/media_session.h"
+#include "content/browser/media/session/mock_media_session_observer.h"
+#include "content/public/test/content_browser_test.h"
+#include "content/shell/browser/shell.h"
+#include "media/base/media_switches.h"
+
+namespace content {
+
+class MediaSessionDelegateDefaultBrowserTest : public ContentBrowserTest {
+ protected:
+  void SetUpCommandLine(base::CommandLine* command_line) override {
+    command_line->AppendSwitch(switches::kEnableDefaultMediaSession);
+  }
+};
+
+IN_PROC_BROWSER_TEST_F(MediaSessionDelegateDefaultBrowserTest,
+                       ActiveWebContentsPauseOthers) {
+  scoped_ptr<MockMediaSessionObserver> media_session_observer(
+      new MockMediaSessionObserver);
+
+  MediaSession* media_session = MediaSession::Get(shell()->web_contents());
+  ASSERT_TRUE(media_session);
+
+  WebContents* other_web_contents = CreateBrowser()->web_contents();
+  MediaSession* other_media_session = MediaSession::Get(other_web_contents);
+  ASSERT_TRUE(other_media_session);
+
+  media_session_observer->StartNewPlayer();
+  media_session->AddPlayer(
+      media_session_observer.get(), 0, MediaSession::Type::Content);
+  EXPECT_TRUE(media_session->IsActive());
+  EXPECT_FALSE(other_media_session->IsActive());
+
+  media_session_observer->StartNewPlayer();
+  other_media_session->AddPlayer(
+      media_session_observer.get(), 1, MediaSession::Type::Content);
+  EXPECT_FALSE(media_session->IsActive());
+  EXPECT_TRUE(other_media_session->IsActive());
+
+  media_session->Stop(MediaSession::SuspendType::UI);
+  other_media_session->Stop(MediaSession::SuspendType::UI);
+}
+
+}  // namespace content