media: Add MojoCdmServiceContext.

media/base/cdm_context.h

Index: media/base/cdm_context.h
diff --git a/media/base/cdm_context.h b/media/base/cdm_context.h
index a0861c4e5db41359f0e877c5ebce59008fde5c9d..356e276acf364227a50f27b08a5fa0ee1f1cbdc7 100644
--- a/media/base/cdm_context.h
+++ b/media/base/cdm_context.h
@@ -41,6 +41,27 @@ class MEDIA_EXPORT CdmContext {
   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;