[Android,VideoFling] Never add null players to alternative ones

chrome/browser/media/android/remote/remote_media_player_manager.cc

Index: chrome/browser/media/android/remote/remote_media_player_manager.cc
diff --git a/chrome/browser/media/android/remote/remote_media_player_manager.cc b/chrome/browser/media/android/remote/remote_media_player_manager.cc
index 90b70ea60454f890deffdc2cdd9d74a486e4b345..461555866fe00c4ad1411c6aad2e4491a2607e89 100644
--- a/chrome/browser/media/android/remote/remote_media_player_manager.cc
+++ b/chrome/browser/media/android/remote/remote_media_player_manager.cc
@@ -143,13 +143,20 @@ RemoteMediaPlayerBridge* RemoteMediaPlayerManager::CreateRemoteMediaPlayer(
 }
 
 void RemoteMediaPlayerManager::SwapCurrentPlayer(int player_id) {
-  // Find the remote player
+  // Find the alternative player to swap the current one with.
   auto it = GetAlternativePlayer(player_id);
   if (it == alternative_players_.end())
     return;
+
   MediaPlayerAndroid* new_player = *it;
   std::unique_ptr<MediaPlayerAndroid> old_player =
       SwapPlayer(player_id, new_player);
+  if (!old_player) {
+    // There's no player to swap with, destroy the alternative player and exit.
+    alternative_players_.erase(it);

[aberent, 2016/04/18 15:31:46]

Does this now need a change to SwitchToRemotePlayer to handle this case?
SwitchToRemotePlayer seems to assume that SwapCurrentPlayer works correctly, and
doesn't check that it has a new valid player before starting remote playback.

If the error case can never happen when the call is from SwitchToRemotePlayer
then maybe we should inline this function and only handle the error case in
SwitchToLocalPlayer.

The real answer to this mess is, of course, to merge remote_media_player_manager
into browser_media_player_manager, but that is a much bigger job.

[whywhat, 2016/04/18 16:50:46]

Done. Added a check. Doesn't seem to be necessary in other two places where
SwapCurrentPlayer is called (for SwitchToLocalPlayer the check would be a no-op,
for ReplaceRemotePlayerWithLocal it would crash earlier if one of the players
were missing or null.

+    return;
+  }
+
   alternative_players_.weak_erase(it);
   alternative_players_.push_back(old_player.release());
 }