Platforms inconsistently clear/don't clear surface before root layer

```
From: https://groups.google.com/forum/#!topic/gwt-forplay/rHbpUHECLKw

HTML GL and Android clear the surface before painting the root layer, while 
Flash and Java don't. Platforms should consistently clear the surface to rgba 
(0,0,0,0) before painting the root layer.
```

Original issue reported on code.google.com by `mmast...@gmail.com` on 24 Jun 2011 at 8:06
