media: Supports Clear Key key system for mojo CDM/Renderer combo

media/mojo/clients/mojo_cdm_factory.cc

Index: media/mojo/clients/mojo_cdm_factory.cc
diff --git a/media/mojo/clients/mojo_cdm_factory.cc b/media/mojo/clients/mojo_cdm_factory.cc
index 3837b0f57d238d3b1c0c3b595bf3e17cd2b928ab..7b2da3c8c942f1b4e4752b6760fc719d2d0f2627 100644
--- a/media/mojo/clients/mojo_cdm_factory.cc
+++ b/media/mojo/clients/mojo_cdm_factory.cc
@@ -41,6 +41,12 @@ void MojoCdmFactory::Create(
     return;
   }
 
+// When MojoRenderer is used, the real Renderer is running in a remote process,
+// which cannot use an AesDecryptor running locally. In this case, always
+// create the MojoCdm, giving the remote CDM a chance to handle |key_system|.
+// Note: We should not run AesDecryptor in the browser process except for
+// testing. See http://crbug.com/441957
+#if !defined(ENABLE_MOJO_RENDERER)

[yucliu1, 2016/11/11 21:44:38]

Can we have mojo cdm without mojo renderer?

[xhwang, 2016/11/11 21:45:54]

Yes, MojoCdm can work with the existing local RendererImpl through
MojoDecryptor. This is the plan for desktop CDM.

   if (CanUseAesDecryptor(key_system)) {
     scoped_refptr<MediaKeys> cdm(
         new AesDecryptor(security_origin, session_message_cb, session_closed_cb,

[yucliu1, 2016/11/12 00:26:24]

I remember the AesDecryptor::GetCdmId returns kInvalidCdmId which may breaks
some assumption:

https://cs.chromium.org/chromium/src/media/mojo/clients/mojo_audio_decoder.cc...

https://cs.chromium.org/chromium/src/media/filters/gpu_video_decoder.cc?sq=pa...

[xhwang, 2016/11/12 00:30:01]

These are all remote decoders, which will not work with AesDecryptor directly.
In this cease, usually we use DecryptingDemuxerStream to decrypt in the render
process directly, then what the decoders get will be clear (unencrypted) stream:

https://cs.chromium.org/chromium/src/media/filters/decoder_selector.cc?rcl=0&...

@@ -49,6 +55,7 @@ void MojoCdmFactory::Create(
         FROM_HERE, base::Bind(cdm_created_cb, cdm, ""));
     return;
   }
+#endif
 
   mojom::ContentDecryptionModulePtr cdm_ptr;
   service_manager::GetInterface<mojom::ContentDecryptionModule>(