Revert of remvoe duplicate impl for SkImageInfo flattening

include/core/SkBitmapDevice.h

Index: include/core/SkBitmapDevice.h
diff --git a/include/core/SkBitmapDevice.h b/include/core/SkBitmapDevice.h
index f3d40d0ce8d9ca53102fb360b0b76e5cd799e59c..83f480c60c21baf5e883abcac98f1f45977df071 100644
--- a/include/core/SkBitmapDevice.h
+++ b/include/core/SkBitmapDevice.h
@@ -258,8 +258,6 @@
 
     friend class SkSurface_Raster;
 
-    void init(SkBitmap::Config config, int width, int height, bool isOpaque);
-
     // used to change the backend's pixels (and possibly config/rowbytes)
     // but cannot change the width/height, so there should be no change to
     // any clip information.