make SkDevice constructors explicit between offscreen and on/direct

http://codereview.appspot.com/4632044/



git-svn-id: http://skia.googlecode.com/svn/trunk@1620 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/views/SkWindow.cpp b/src/views/SkWindow.cpp
index db4faee..dc833ec 100644
--- a/src/views/SkWindow.cpp
+++ b/src/views/SkWindow.cpp
@@ -172,11 +172,8 @@
 
         if (NULL == canvas) {
             canvas = &rasterCanvas;
-            device = new SkDevice(canvas, bm, false);
-            canvas->setDevice(device)->unref();
-        } else {
-            canvas->setBitmapDevice(bm);
         }
+        canvas->setBitmapDevice(bm);
 
 		canvas->clipRegion(fDirtyRgn);
 		if (updateArea)