Add PlayerTracker and BrowserCdm interfaces.

media/base/player_tracker.h

Index: media/base/player_tracker.h
diff --git a/media/base/player_tracker.h b/media/base/player_tracker.h
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+++ b/media/base/player_tracker.h
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+// 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 that helps CDMs notify players when a new decryption key becomes

[ddorwin, 2014/05/30 20:50:05]

nit: "An interface for players to register to be notified when..."

[xhwang, 2014/06/02 20:11:43]

Done.

+// available or when the CDM is destroyed.
+class MEDIA_EXPORT PlayerTracker {
+ public:
+  PlayerTracker();

[ddorwin, 2014/05/30 20:50:05]

ditto

[xhwang, 2014/06/02 20:11:43]

Done.

+  virtual ~PlayerTracker();
+
+  // Registers player callbacks with the CDM.
+  // - |new_key_cb| is fired when a new decryption key becomes available.
+  // - |cdm_destroyed_cb| is fired when the CDM is destroyed.

[ddorwin, 2014/05/30 20:50:05]

ditto on the name

[xhwang, 2014/06/02 20:11:43]

Done.

+  // 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_destroyed_cb) = 0;

[damienv1, 2014/05/30 15:10:15]

There is an implicit assumption that the CDM and the player are running on the
same thread here (which is ok to me), but this might not apply to every use
case.
By the time the notification is received on the other thread, the CDM can
already be destroyed.

[xhwang, 2014/05/30 17:18:53]

The current plan is to use this only for BrowserCdm. So this simple model will
work fine. We need to work out a long term plan for CDM/player tracking for
desktop.

[ddorwin, 2014/05/30 20:50:05]

Can we add DCHECKs on the thread?

[xhwang, 2014/06/02 20:11:43]

Done.

+
+  // 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;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(PlayerTracker);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_PLAYER_TRACKER_H_