Add quotation marks around enums in shaka.text.Cue
Add quotation marks around enums in shaka.text.Cue

Text parsers set several cue enum properties with
parsedValue.toUpper() rather than explicitely stating the enum
value. Renaming enum keys in compiled mode interferes with it.

Closes #987

Change-Id: Id3ff878eaa96bce28eaddd379a457f8743c97ea2

shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,vimond/shaka-player,tvoli/shaka-player,TheModMaker/shaka-player,vimond/shaka-player,tvoli/shaka-player,TheModMaker/shaka-player,tvoli/shaka-player,TheModMaker/shaka-player,TheModMaker/shaka-player,vimond/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player