Make GM render to render targets that are also textures.

include/gpu/SkGpuDevice.h

Index: include/gpu/SkGpuDevice.h
===================================================================
--- include/gpu/SkGpuDevice.h	(revision 8437)
+++ include/gpu/SkGpuDevice.h	(working copy)
@@ -27,16 +27,24 @@
  */
 class SK_API SkGpuDevice : public SkDevice {
 public:
+
     /**
+     * Creates an SkGpuDevice from a GrSurface. This will fail if the surface is not a render
+     * target. The caller owns a ref on the returned device.
+     */
+    static SkGpuDevice* Create(GrSurface* surface);
+
+    /**
      *  New device that will create an offscreen renderTarget based on the
      *  config, width, height, and sampleCount. The device's storage will not
      *  count against the GrContext's texture cache budget. The device's pixels
-     *  will be uninitialized.
+     *  will be uninitialized. TODO: This can fail, replace with a factory function.
      */
     SkGpuDevice(GrContext*, SkBitmap::Config, int width, int height, int sampleCount = 0);
 
     /**
      *  New device that will render to the specified renderTarget.
+     *  DEPRECATED: Use Create(surface)
      */
     SkGpuDevice(GrContext*, GrRenderTarget*);
 
@@ -44,6 +52,7 @@
      *  New device that will render to the texture (as a rendertarget).
      *  The GrTexture's asRenderTarget() must be non-NULL or device will not
      *  function.
+     *  DEPRECATED: Use Create(surface)
      */
     SkGpuDevice(GrContext*, GrTexture*);