Add more out of line copy ctors for complex classes.

cc/tiles/software_image_decode_controller.h

Index: cc/tiles/software_image_decode_controller.h
diff --git a/cc/tiles/software_image_decode_controller.h b/cc/tiles/software_image_decode_controller.h
index 54d655e690a2004bf081ac599c881d1da6b7d006..4e959c7f2f8deae238e8e1e1bd9b4435c12e29ff 100644
--- a/cc/tiles/software_image_decode_controller.h
+++ b/cc/tiles/software_image_decode_controller.h
@@ -33,6 +33,8 @@ class CC_EXPORT ImageDecodeControllerKey {
  public:
   static ImageDecodeControllerKey FromDrawImage(const DrawImage& image);
 
+  ImageDecodeControllerKey(const ImageDecodeControllerKey& other);
+
   bool operator==(const ImageDecodeControllerKey& other) const {
     // The image_id always has to be the same. However, after that all original
     // decodes are the same, so if we can use the original decode, return true.