added a TODO to handle bad element ids

Change-Id: I73457a9a7644b747efcdc745eeac0bca48ad1bd1
diff --git a/webm.py b/webm.py
index 9bde3da..cd70ec5 100644
--- a/webm.py
+++ b/webm.py
@@ -185,6 +185,7 @@
   start_pos = pos
   size, pos = ReadOneByteForElementIdSize(file_, pos)
   element_id, pos = ProcessIdSize(file_, pos, size)
+ # TODO(hwasoo): need to check element id
 
   data_size_length, pos = ReadOneByteForDataSize(file_, pos)
   assert data_size_length > 0