media: Support creation and SetCdm() for mojo based CDM.

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"
@@ skipping 23 matching lines @@
   // supports a Decryptor interface.
   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|.
+// This is typically used when CDMs are hosted remotely.
+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 irrelevant to GetCdmId() of the returned CdmContext.

[ddorwin, 2015/05/15 19:10:07]

This is hard to understand. Perhaps they are not necessarily the same? And
|cdm_id| is for X while GetCdmId() is Y?

[xhwang, 2015/06/01 21:21:24]

Updated comment with more restrictions.

+  // The former is used to locate the real CDM (the latter), which could just
+  // be a local CDM that doesn't support a CDM ID.
+  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_