Use std::string for decryption key ID in webm parser.

media/webm/webm_tracks_parser.cc

Index: media/webm/webm_tracks_parser.cc
diff --git a/media/webm/webm_tracks_parser.cc b/media/webm/webm_tracks_parser.cc
index 29c8f2fafeb5e8e7b124e940a1c5862e78579d9d..bf039bf77bde53870e56cc3d0564cebde0c74762 100644
--- a/media/webm/webm_tracks_parser.cc
+++ b/media/webm/webm_tracks_parser.cc
@@ -25,24 +25,15 @@ WebMTracksParser::WebMTracksParser()
 
 WebMTracksParser::~WebMTracksParser() {}
 
-const uint8* WebMTracksParser::video_encryption_key_id() const {
+const std::string& WebMTracksParser::video_encryption_key_id() const {
   if (!video_content_encodings_client_.get())
-    return NULL;
+    return EmptyString();
 
   DCHECK(!video_content_encodings_client_->content_encodings().empty());
   return video_content_encodings_client_->content_encodings()[0]->
       encryption_key_id();
 }
 
-int WebMTracksParser::video_encryption_key_id_size() const {
-  if (!video_content_encodings_client_.get())
-    return 0;
-
-  DCHECK(!video_content_encodings_client_->content_encodings().empty());
-  return video_content_encodings_client_->content_encodings()[0]->
-      encryption_key_id_size();
-}
-
 int WebMTracksParser::Parse(const uint8* buf, int size) {
   track_type_ =-1;
   track_num_ = -1;