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.
+  virtual void* GetClassIdentifier() const;
+
  protected:
   CdmContext();