media: Add MediaDrmBridgeCdmContext.

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 82e088d1200813a25e5008432461442db54324e0..4ad703aa2756c6941b1e52093e2427c2dd6e785a 100644
--- a/media/base/cdm_context.h
+++ b/media/base/cdm_context.h
@@ -13,9 +13,9 @@ namespace media {
 
 class Decryptor;
 
-// An interface representing the context that a media pipeline needs from a
+// An interface representing the context that a media player needs from a
 // content decryption module (CDM) to decrypt (and decode) encrypted buffers.
-// Only used for implementing SetCdm().
+// This is used to pass the CDM to the media player (e.g. SetCdm()).
 class MEDIA_EXPORT CdmContext {
  public:
   // Indicates an invalid CDM ID. See GetCdmId() for details.
@@ -24,15 +24,13 @@ class MEDIA_EXPORT CdmContext {
   virtual ~CdmContext();
 
   // 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.
+  // CDM does not support a Decryptor. The returned object is only guaranteed to

[ddorwin, 2016/03/22 17:20:12]

nit: Should we add something like "(i.e. platform-based CDMs where decryption
occurs implicitly along with decoding)"?

[xhwang, 2016/03/22 17:35:10]

Done.

+  // be valid during the CDM's lifetime.
   virtual Decryptor* GetDecryptor() = 0;
 
-  // 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.
+  // Returns an ID that can be used to identify a CDM remotely, in which case

[ddorwin, 2016/03/22 17:20:12]

nit: I'm not sure what "identify... remotely" means. "remote CDM" may be
sufficient.

[xhwang, 2016/03/22 17:35:10]

Done.

+  // this CDM serves as a proxy to the remote CDM. Returns kInvalidCdmId when
+  // remote CDM is not supported (e.g. this CDM is a concrete CDM).

[ddorwin, 2016/03/22 17:20:12]

nit: I'm not sure what a "concrete CDM" is. Perhaps "this object directly
represents the CDM" or something like that.

[xhwang, 2016/03/22 17:35:10]

Done. Used "local" in comparison to "remote".

   virtual int GetCdmId() const = 0;
 
  protected: