Add more out of line copy ctors for complex classes.

cc/tiles/software_image_decode_controller.cc

Index: cc/tiles/software_image_decode_controller.cc
diff --git a/cc/tiles/software_image_decode_controller.cc b/cc/tiles/software_image_decode_controller.cc
index d1e7f8083c497b3cd526ee36975cda02d00501d3..96f5618a48f3d8e79a3b7fe343562e54643bfbf7 100644
--- a/cc/tiles/software_image_decode_controller.cc
+++ b/cc/tiles/software_image_decode_controller.cc
@@ -821,6 +821,9 @@ ImageDecodeControllerKey::ImageDecodeControllerKey(
   }
 }
 
+ImageDecodeControllerKey::ImageDecodeControllerKey(
+    const ImageDecodeControllerKey& other) = default;
+
 std::string ImageDecodeControllerKey::ToString() const {
   std::ostringstream str;
   str << "id[" << image_id_ << "] src_rect[" << src_rect_.x() << ","