media: Add MojoCdmServiceContext.

media/base/cdm_context.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_CDM_CONTEXT_H_
 #define MEDIA_BASE_CDM_CONTEXT_H_
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "media/base/media_export.h"
 
 namespace media {
 
 class Decryptor;
 
 // An interface representing the context that a media pipeline needs from a
 // content decryption module (CDM) to decrypt (and decode) encrypted buffers.

[sandersd (OOO until July 31), 2015/06/04 22:53:07]

Add that CdmContext is only used for calling SetCdm().

[xhwang, 2015/06/05 18:14:52]

Done.

 class MEDIA_EXPORT CdmContext {
  public:
   // Indicates an invalid CDM ID. See GetCdmId() for details.
   static const int kInvalidCdmId = 0;
 
   virtual ~CdmContext();
 
   // Gets the Decryptor object associated with the CDM. Returns NULL if the CDM
   // does not support a Decryptor. The returned object is only guaranteed to be
   // valid during the CDM's lifetime.

[sandersd (OOO until July 31), 2015/06/04 22:53:07]

Add that if the return value will not be NULL if GetCdmId() is kInvalidCdm.

[xhwang, 2015/06/05 18:14:51]

Done.

   virtual Decryptor* GetDecryptor() = 0;
 
   // Returns an ID associated with the CDM, which can be used to locate the real
   // CDM instance. This is useful when the CDM is hosted remotely, e.g. in a
   // different process.

[sandersd (OOO until July 31), 2015/06/04 22:53:07]

This sentence is confusing. I would say:

Returns an ID that identifies a CDM, or kInvalidCdmId. The interpretation is
implementation-specific; current implementations use the ID to locate a remote
CDM in the browser process.

[xhwang, 2015/06/05 18:14:51]

Done with s/the browser/a different/ because we can host a CDM in any process
(e.g. gpu, utility...)

   // Returns kInvalidCdmId if the CDM cannot be used remotely. In this case,
   // GetDecryptor() should return a non-null Decryptor.

[sandersd (OOO until July 31), 2015/06/04 22:53:07]

I would say:

The return value will not be kInvalidCdm if GetDecryptor() returns NULL.

[xhwang, 2015/06/05 18:14:52]

Done.

   virtual int GetCdmId() const = 0;
 
  protected:
   CdmContext();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CdmContext);
 };
 
+// An interface that provides the access to a CdmContext through |cdm_id|.

[sandersd (OOO until July 31), 2015/06/04 22:53:07]

An interface for looking up CdmContext objects by |cdm_id|.

[xhwang, 2015/06/05 18:14:51]

Done.

+// This is typically used when CDMs are hosted remotely.

[sandersd (OOO until July 31), 2015/06/04 22:53:07]

This is confusing because a CdmContextProvider only locates CDMs that are local
(to the caller). I would just remove it.

[xhwang, 2015/06/05 18:14:52]

Done.

+class MEDIA_EXPORT CdmContextProvider {
+ public:
+  virtual ~CdmContextProvider();
+
+  // Returns the CdmContext corresponding to |cdm_id|. Returns nullptr if no
+  // such CdmContext can be found.
+  // Note: |cdm_id| is not necessarily the same as GetCdmId() of the returned
+  // CdmContext. The former is used to locate the real CDM, which typically
+  // is a local CDM and cannot be used remotely. So GetCdmId() on the returned
+  // CdmContext should return kInvalidCdmId.

[sandersd (OOO until July 31), 2015/06/04 22:53:07]

I would say:

Note: Calling GetCdmId() on the returned CdmContext returns kInvalidCdmId (in
all current cases) because the CDM will be local.

[xhwang, 2015/06/05 18:14:52]

Done.

+  virtual CdmContext* GetCdmContext(int cdm_id) = 0;
+
+ protected:
+  CdmContextProvider();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(CdmContextProvider);
+};
+
 // Callback to notify that the CdmContext has been completely attached to
 // the media pipeline. Parameter indicates whether the operation succeeded.
 typedef base::Callback<void(bool)> CdmAttachedCB;
 
 // A dummy implementation of CdmAttachedCB.
 MEDIA_EXPORT void IgnoreCdmAttached(bool success);
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_CDM_CONTEXT_H_