Remove include of SkGLDevice.h from SkGLCanvas.h

Remove include of SkGLDevice.h from SkGLCanvas.h

The '#include "SkGLDevice.h"' from include/core/SkDevice.h requires internal
Skia code to be added to the include search paths when using the deprecated API.
This change adds back SkGLCanvas.cpp to avoid exposing SkGLDevice.h to the
public API.

The change also includes an explicit virtual destructor on SkDeviceFactory to
silence a -Wnon-virtual-dtor warning and allow for -Werror.

Original Issue: http://codereview.appspot.com/3009041/

Committed: http://code.google.com/p/skia/source/detail?r=623