Expose SkPicture::numSlowPaths() in the public API.

src/core/SkBigPicture.h

Index: src/core/SkBigPicture.h
diff --git a/src/core/SkBigPicture.h b/src/core/SkBigPicture.h
index b081855751fbe4f1c1d10bf643d59b32ab3e52e7..b227fc892f7f44f4b0d7cfe9a500eafbfe1fb17c 100644
--- a/src/core/SkBigPicture.h
+++ b/src/core/SkBigPicture.h
@@ -51,6 +51,7 @@ public:
     int approximateOpCount() const override;
     size_t approximateBytesUsed() const override;
     const SkBigPicture* asSkBigPicture() const override { return this; }
+    int numSlowPaths() const override;
 
 // Used by GrLayerHoister
     void partialPlayback(SkCanvas*,
@@ -72,7 +73,6 @@ private:
         bool    fWillPlaybackBitmaps : 1;
     };
 
-    int numSlowPaths() const override;
     const Analysis& analysis() const;
     int drawableCount() const;
     SkPicture const* const* drawablePicts() const;