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.
+// Only used for implementing SetCdm().
 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.
+  // Gets the Decryptor object associated with the CDM. Returns nullptr if the
+  // CDM does not support a Decryptor. Must not return nullptr if GetCdmId()
+  // returns kInvalidCdmId. The returned object is only guaranteed to be valid
+  // during the CDM's lifetime.
   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.
-  // Returns kInvalidCdmId if the CDM cannot be used remotely. In this case,
-  // GetDecryptor() should return a non-null Decryptor.
+  // 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 a different process. The return value will not be
+  // kInvalidCdmId if GetDecryptor() returns nullptr.
   virtual int GetCdmId() const = 0;
 
  protected:
   CdmContext();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CdmContext);
 };
 
+// An interface for looking up CdmContext objects by the CDM ID.
+class MEDIA_EXPORT CdmContextProvider {
+ public:
+  virtual ~CdmContextProvider();
+
+  // Returns the CdmContext corresponding to |cdm_id|. Returns nullptr if no
+  // such CdmContext can be found.
+  // Note: Calling GetCdmId() on the returned CdmContext returns kInvalidCdmId
+  // (in all current cases) because the CDM will be local in the process where
+  // GetCdmContext() is called.
+  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_