I recommend temporarily disabling web workers, which should provide better visibility into js bottlenecks in tools such as Chrome's timeline panel [1]. Also check out this google IO talk [2] on performance debugging the WebGL/HTML5 demo "Find Your Way to Oz" [3].
[1] https://developers.google.com/chrome-developer-tools/docs/ti...
[2] https://developers.google.com/events/io/sessions/324908972