MSE: Protect better against out-of-sequence parser callbacks

media/filters/media_source_state.h

Index: media/filters/media_source_state.h
diff --git a/media/filters/media_source_state.h b/media/filters/media_source_state.h
index e6878f6071ce9efe5ac11232970f01395d60a43a..89974a6b506e2971566d840439232bafc411b1e7 100644
--- a/media/filters/media_source_state.h
+++ b/media/filters/media_source_state.h
@@ -116,6 +116,16 @@ class MEDIA_EXPORT MediaSourceState {
   void SetTracksWatcher(const Demuxer::MediaTracksUpdatedCB& tracks_updated_cb);
 
  private:
+  // State advances through this list. The intent is to ensure at least one
+  // config is received prior to parser calling initialization callback, and
+  // that such initialization callback occurs at most once per parser.
+  enum State {
+    UNINITIALIZED = 0,
+    PENDING_PARSER_CONFIG,
+    PENDING_PARSER_INIT,
+    PARSER_INITIALIZED
+  };
+
   // Called by the |stream_parser_| when a new initialization segment is
   // encountered.
   // Returns true on a successful call. Returns false if an error occurred while
@@ -192,6 +202,8 @@ class MEDIA_EXPORT MediaSourceState {
   scoped_refptr<MediaLog> media_log_;
   StreamParser::InitCB init_cb_;
 
+  State state_;
+
   // During Append(), OnNewConfigs() will trigger the initialization segment
   // received algorithm. Note, the MSE spec explicitly disallows this algorithm
   // during an Abort(), since Abort() is allowed only to emit coded frames, and