add saveBehind to canvas

Bug: skia:
Change-Id: I62e48b116b2d7efef585d4f465441f24ae4d2b29
Reviewed-on: https://skia-review.googlesource.com/c/177892
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/tools/debugger/SkDebugCanvas.h b/tools/debugger/SkDebugCanvas.h
index ca54415..2a5c3de 100644
--- a/tools/debugger/SkDebugCanvas.h
+++ b/tools/debugger/SkDebugCanvas.h
@@ -113,9 +113,8 @@
 
 protected:
     void willSave() override;
-
     SaveLayerStrategy getSaveLayerStrategy(const SaveLayerRec &) override;
-
+    bool onDoSaveBehind(const SkRect*) override;
     void willRestore() override;
 
     void didConcat(const SkMatrix &) override;