Make MediaSession a runtime-enabled feature on Desktop.

content/content_tests.gypi

Index: content/content_tests.gypi
diff --git a/content/content_tests.gypi b/content/content_tests.gypi
index 23710bd279db38305155d80b83b414b01203b28b..74e4ffb56eeff3ca6413f8513c94eb6057cb372b 100644
--- a/content/content_tests.gypi
+++ b/content/content_tests.gypi
@@ -232,12 +232,15 @@
       'browser/loader/cross_site_resource_handler_browsertest.cc',
       'browser/loader/resource_dispatcher_host_browsertest.cc',
       'browser/manifest/manifest_browsertest.cc',
-      'browser/media/android/media_session_browsertest.cc',
       'browser/media/encrypted_media_browsertest.cc',
       'browser/media/media_browsertest.cc',
       'browser/media/media_browsertest.h',
       'browser/media/media_canplaytype_browsertest.cc',
       'browser/media/media_source_browsertest.cc',
+      'browser/media/session/media_session_browsertest.cc',
+      'browser/media/session/media_session_delegate_default_browsertest.cc',
+      'browser/media/session/mock_media_session_observer.cc',
+      'browser/media/session/mock_media_session_observer.h',
       'browser/memory/memory_pressure_controller_impl_browsertest.cc',
       'browser/message_port_provider_browsertest.cc',
       'browser/mojo_shell_browsertest.cc',
@@ -501,8 +504,6 @@
       'browser/loader/temporary_file_stream_unittest.cc',
       'browser/loader/upload_data_stream_builder_unittest.cc',
       'browser/mach_broker_mac_unittest.cc',
-      'browser/media/android/media_session_controller_unittest.cc',
-      'browser/media/android/media_session_uma_helper_unittest.cc',
       'browser/media/audible_metrics_unittest.cc',
       'browser/media/audio_stream_monitor_unittest.cc',
       'browser/media/capture/audio_mirroring_manager_unittest.cc',
@@ -511,6 +512,8 @@
       'browser/media/capture/web_contents_video_capture_device_unittest.cc',
       'browser/media/media_internals_unittest.cc',
       'browser/media/midi_host_unittest.cc',
+      'browser/media/session/media_session_controller_unittest.cc',
+      'browser/media/session/media_session_uma_helper_unittest.cc',
       'browser/media/webrtc/webrtc_identity_store_unittest.cc',
       'browser/net/quota_policy_cookie_store_unittest.cc',
       'browser/notification_service_impl_unittest.cc',
@@ -1580,6 +1583,7 @@
               'sources': [ '<@(content_browsertests_android_sources)' ],
               'sources!': [
                 'browser/battery_status/battery_monitor_impl_browsertest.cc',
+                'browser/media/session/media_session_delegate_default_browsertest.cc',
               ],
               'dependencies': [
                 'content_shell_jni_headers',