add backdrop option to SaveLayerRec

include/core/SkCanvas.h

Index: include/core/SkCanvas.h
diff --git a/include/core/SkCanvas.h b/include/core/SkCanvas.h
index d046b8ef4c99dc007860defc68670dec319152f3..d1de626315ee52503517eb84c83e4de231130b64 100644
--- a/include/core/SkCanvas.h
+++ b/include/core/SkCanvas.h
@@ -422,16 +422,27 @@ public:
     typedef uint32_t SaveLayerFlags;
 
     struct SaveLayerRec {
-        SaveLayerRec() : fBounds(nullptr), fPaint(nullptr), fSaveLayerFlags(0) {}
+        SaveLayerRec()
+            : fBounds(nullptr), fPaint(nullptr), fBackdrop(nullptr), fSaveLayerFlags(0)
+        {}
         SaveLayerRec(const SkRect* bounds, const SkPaint* paint, SaveLayerFlags saveLayerFlags = 0)
             : fBounds(bounds)
             , fPaint(paint)
+            , fBackdrop(nullptr)
+            , fSaveLayerFlags(saveLayerFlags)
+        {}
+        SaveLayerRec(const SkRect* bounds, const SkPaint* paint, const SkImageFilter* backdrop,
+                     SaveLayerFlags saveLayerFlags)
+            : fBounds(bounds)
+            , fPaint(paint)
+            , fBackdrop(backdrop)
             , fSaveLayerFlags(saveLayerFlags)
         {}
 
-        const SkRect*   fBounds;    // optional
-        const SkPaint*  fPaint;     // optional
-        SaveLayerFlags  fSaveLayerFlags;
+        const SkRect*           fBounds;    // optional
+        const SkPaint*          fPaint;     // optional
+        const SkImageFilter*    fBackdrop;  // optional
+        SaveLayerFlags          fSaveLayerFlags;
     };
 
     int saveLayer(const SaveLayerRec&);