cc: Optimize ImageDecodeCacheKey::FromDrawImage.

cc/playback/draw_image.h

Index: cc/playback/draw_image.h
diff --git a/cc/playback/draw_image.h b/cc/playback/draw_image.h
index 878f88ee23a2fa0da9296280c9b958eac4696078..d3633e0114156cdf2d31cd4a91c8b40ccc393709 100644
--- a/cc/playback/draw_image.h
+++ b/cc/playback/draw_image.h
@@ -29,7 +29,7 @@ class CC_EXPORT DrawImage {
 
   const sk_sp<const SkImage>& image() const { return image_; }
   const SkSize& scale() const { return scale_; }
-  const SkIRect src_rect() const { return src_rect_; }
+  const SkIRect& src_rect() const { return src_rect_; }
   SkFilterQuality filter_quality() const { return filter_quality_; }
   bool matrix_is_decomposable() const { return matrix_is_decomposable_; }
   const SkMatrix& matrix() const { return matrix_; }