Add PlayerTracker and BrowserCdm interfaces.

media/base/player_tracker.h

+// Copyright 2014 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.
+
+#ifndef MEDIA_BASE_PLAYER_TRACKER_H_
+#define MEDIA_BASE_PLAYER_TRACKER_H_
+
+#include "base/basictypes.h"
+#include "base/callback.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+// An interface for players to register to be notified when a new decryption key
+// becomes available or when the CDM is unset.
+class MEDIA_EXPORT PlayerTracker {
+ public:
+  virtual ~PlayerTracker();
+
+  // Registers player callbacks with the CDM.
+  // - |new_key_cb| is fired when a new decryption key becomes available.
+  // - |cdm_unset_cb| is fired when the CDM is detached from the player.

[ddorwin, 2014/06/02 20:20:29]

would s/unset/detached/ be a better name?

[xhwang, 2014/06/02 21:41:22]

I chose "unset" because we have SetCdm(). 

+  // Returns a registration ID which can be used to unregister a player.
+  virtual int RegisterPlayer(const base::Closure& new_key_cb,
+                             const base::Closure& cdm_unset_cb) = 0;
+
+  // Unregisters a previously registered player. This should be called when
+  // the CDM is detached from the player (e.g. setMediaKeys(0)), or when the
+  // player is destroyed.
+  virtual void UnregisterPlayer(int registration_id) = 0;
+
+ protected:
+  PlayerTracker();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(PlayerTracker);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_PLAYER_TRACKER_H_