Chrome CZML Image Material Memory?

Greetings Cesium Folks!

I've located some sort of strange memory exhaustion condition in the latest Google Chrome x64 [using this Sandcastle example](https://cesiumjs.org/Cesium/Apps/Sandcastle/?src=Hello%20World.html&label=Showcases&gist=8d5057c17012d79e4585531597e0d453).

If the animation is permitted to run for > 60 seconds, memory use climbs until a rendering crash is observed (on 8GB RAM), and a reload is required. This behavior does not occur in Firefox, IE11 or IE Edge on my test systems.

If there is some sort of issue with how I have my CZML structured which would be causing this, please let me know. I've also [posted this to the folks in the community forum](https://groups.google.com/forum/#!topic/cesium-dev/6brTZBpn0zM) for additional input.

Start by reproducing the linked Sandcastle Hello World example in Chrome with the reported CZML animation running for more than 60 seconds, then compare memory behavior with Firefox, IE11, and Edge. Use the linked community-forum discussion for existing observations; done means identifying the cause of the memory growth or confirming the issue with enough evidence to guide a fix.

Written by the indexing model from the issue text.