Fix minor memory leaks

gm/shallowgradient.cpp

Index: gm/shallowgradient.cpp
===================================================================
--- gm/shallowgradient.cpp	(revision 8402)
+++ gm/shallowgradient.cpp	(working copy)
@@ -58,7 +58,7 @@
         SkSize size = SkSize::Make(r.width(), r.height());
 
         SkPaint paint;
-        paint.setShader(fProc(colors, colorCount, size));
+        paint.setShader(fProc(colors, colorCount, size))->unref();
         canvas->drawRect(r, paint);
     }