Make the canvas draw looper internal layer not part of SkCanvas save count

include/core/SkDrawLooper.h

Index: include/core/SkDrawLooper.h
diff --git a/include/core/SkDrawLooper.h b/include/core/SkDrawLooper.h
index ec070467a5aaecd2b2922173d09e0dcdd6e9f21f..9c6c8df69e4d76f2e53739e052b6deafd16ef7f2 100644
--- a/include/core/SkDrawLooper.h
+++ b/include/core/SkDrawLooper.h
@@ -56,6 +56,11 @@ public:
          *  The implementation must ensure that, when next() finally returns
          *  false, the canvas has been restored to the state it was
          *  initially, before createContext() was first called.
+         *
+         *  It is an error to call SkCanvas::restore() or SkCanvas::restoreToCount on the canvas
+         *  from this function, unless corresponding SkCanvas::save() or SkCanvas::saveLayer() has
+         *  been called. The corresponding save call must be made from this function, but it may be
+         *  made from earlier invocation.
          */
         virtual bool next(SkCanvas* canvas, SkPaint* paint) = 0;
     };