Media Remoting: Add remoting control logic for encrypted contents.

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 d046927c72079fe8956dd104a9a3a5c9cb254422..65c0bb7a6963100b7cf88a2c8c838b7172225d07 100644
--- a/media/base/cdm_context.h
+++ b/media/base/cdm_context.h
@@ -34,6 +34,10 @@ class MEDIA_EXPORT CdmContext {
   // is not supported (e.g. this CDM is a local CDM).
   virtual int GetCdmId() const = 0;
 
+  // Returns a unique class identifier. Some subclasses override and use this
+  // method to provide safe down-casting to their type.

[xhwang, 2016/11/01 08:21:28]

If I add a new CdmContext, how should I implement this method?

[xjz, 2016/11/01 21:55:52]

The implementation of this is up to each implementation of CdmContext. If not
implemented, this will return null ptr by default.

[xhwang, 2016/11/02 06:47:05]

+miu

But how "unique" is unique? The current impl only guarantees that the "id" will
be unique in the current process.  Two instances of the same CDM running in two
processes would could get two different ID, and two different CDMs could get the
same ID when running in two processes (though the chance is low)...

I guess a normal developer have to look at how RemotingCdm implements this to be
able to implement this in another CDM, which means this interface isn't complete
form an API's perspective.

+  virtual void* GetClassIdentifier() const;

[xhwang, 2016/11/01 08:21:28]

Please see my comment in remoting_cdm.cc about the class ID.

[xjz, 2016/11/01 21:55:52]

Replied to that comment. :)

+
  protected:
   CdmContext();