Make gpu work in iOS SampleApp.

This includes updates to the GrGLInterface and changes to the DeviceManager subclass used on iOS.
Review URL: https://codereview.appspot.com/6582043

git-svn-id: http://skia.googlecode.com/svn/trunk@5722 2bbb7eff-a529-9590-31e7-b0007b416f81
4 files changed