Add validation check to GrGpu::createTexture & minor SkGpuDevice cleanup

https://codereview.appspot.com/6821055/



git-svn-id: http://skia.googlecode.com/svn/trunk@6213 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/gpu/SkGpuDevice.h b/include/gpu/SkGpuDevice.h
index a1d00ba..0a5f36e 100644
--- a/include/gpu/SkGpuDevice.h
+++ b/include/gpu/SkGpuDevice.h
@@ -29,11 +29,11 @@
 public:
     /**
      *  New device that will create an offscreen renderTarget based on the
-     *  config, width, height. The device's storage will not count against
-     *  the GrContext's texture cache budget. The device's pixels will be
-     *  uninitialized.
+     *  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.
      */
-    SkGpuDevice(GrContext*, SkBitmap::Config, int width, int height);
+    SkGpuDevice(GrContext*, SkBitmap::Config, int width, int height, int sampleCount = 0);
 
     /**
      *  New device that will render to the specified renderTarget.