Add support for encrypted WebM files as defined in the RFC.

media/webm/webm_stream_parser.cc

Index: media/webm/webm_stream_parser.cc
diff --git a/media/webm/webm_stream_parser.cc b/media/webm/webm_stream_parser.cc
index 602d22787c341b9603d49f317345678dc5f78320..d141bfdd1525cb24cc7a232c62c5487e8d1750f8 100644
--- a/media/webm/webm_stream_parser.cc
+++ b/media/webm/webm_stream_parser.cc
@@ -352,6 +352,7 @@ int WebMStreamParser::ParseInfoAndTracks(const uint8* data, int size) {
   if (tracks_parser.video_encryption_key_id()) {
     int key_id_size = tracks_parser.video_encryption_key_id_size();
     CHECK_GT(key_id_size, 0);
+    CHECK_LT(key_id_size, 2048);
     scoped_array<uint8> key_id(new uint8[key_id_size]);
     memcpy(key_id.get(), tracks_parser.video_encryption_key_id(), key_id_size);
     need_key_cb_.Run(key_id.Pass(), key_id_size);