--- a/image/Downscaler.h
+++ b/image/Downscaler.h
@@ -166,16 +166,17 @@ public:
 
   bool IsFrameComplete() const { return false; }
   uint8_t* RowBuffer() { return nullptr; }
   void ClearRow(uint32_t = 0) { }
   void CommitRow() { }
   bool HasInvalidation() const { return false; }
   DownscalerInvalidRect TakeInvalidRect() { return DownscalerInvalidRect(); }
   void ResetForNextProgressivePass() { }
+  const nsIntSize FrameSize() const { return 0; }
 };
 
 #endif // MOZ_ENABLE_SKIA
 
 
 
 } // namespace image
 } // namespace mozilla