mash: Change the MediaDelegate to a Media{Controller,Client}.

ash/BUILD.gn

Index: ash/BUILD.gn
diff --git a/ash/BUILD.gn b/ash/BUILD.gn
index daf50c665a6e9edc69110489df846112824260a3..4605647e28bef4afafae2c1d70febee4bcdafcc0 100644
--- a/ash/BUILD.gn
+++ b/ash/BUILD.gn
@@ -119,6 +119,8 @@ component("ash") {
     "common/login_status.h",
     "common/material_design/material_design_controller.cc",
     "common/material_design/material_design_controller.h",
+    "common/media_controller.cc",
+    "common/media_controller.h",
     "common/metrics/gesture_action_type.h",
     "common/metrics/pointer_metrics_recorder.cc",
     "common/metrics/pointer_metrics_recorder.h",
@@ -228,7 +230,6 @@ component("ash") {
     "common/system/chromeos/ime_menu/ime_menu_tray.h",
     "common/system/chromeos/keyboard_brightness_controller.cc",
     "common/system/chromeos/keyboard_brightness_controller.h",
-    "common/system/chromeos/media_security/media_capture_observer.h",
     "common/system/chromeos/media_security/multi_profile_media_tray_item.cc",
     "common/system/chromeos/media_security/multi_profile_media_tray_item.h",
     "common/system/chromeos/network/network_detailed_view.h",