Canvas resize error with retina display

Reported on the forum: https://groups.google.com/forum/?hl=en#!topic/cesium-dev/NqW0TnqPDNc

> Check out the following link on iOS/Chrome, or a UIWebView. The device you use should have a retina display. The problem happens in normal Safari too, but it requires more attempts to see it:
>
> http://cloudahoy.com/cesium-basic
>
> When you resize the container (it might take a few tries), the canvas gets into a state where it is rendered too large

I'm thinking this might be related to #3288?

Start by reproducing the issue at http://cloudahoy.com/cesium-basic on a retina iOS/Chrome, UIWebView, or Safari environment, including repeated container resizes, and compare it with the behavior discussed in #3288. Done means the canvas no longer renders larger than its resized container.

Written by the indexing model from the issue text.