Convert between |init_data_type| and content type.

content/renderer/media/crypto/proxy_media_keys.cc

Index: content/renderer/media/crypto/proxy_media_keys.cc
diff --git a/content/renderer/media/crypto/proxy_media_keys.cc b/content/renderer/media/crypto/proxy_media_keys.cc
index 68a68b3bc370f6ca5d00f759da469ad6172fcb20..17e918d80ec2338c847244448525903fa3d047a1 100644
--- a/content/renderer/media/crypto/proxy_media_keys.cc
+++ b/content/renderer/media/crypto/proxy_media_keys.cc
@@ -57,9 +57,9 @@ void ProxyMediaKeys::CreateSession(
   // TODO(xhwang): Move these checks up to blink and DCHECK here.
   // See http://crbug.com/342510
   CdmHostMsg_CreateSession_ContentType create_session_content_type;
-  if (init_data_type == "audio/mp4" || init_data_type == "video/mp4") {
+  if (init_data_type == "cenc") {
     create_session_content_type = CREATE_SESSION_TYPE_MP4;
-  } else if (init_data_type == "audio/webm" || init_data_type == "video/webm") {
+  } else if (init_data_type == "webm") {
     create_session_content_type = CREATE_SESSION_TYPE_WEBM;
   } else {
     DLOG(ERROR) << "Unsupported EME CreateSession content type of "