printing: Add out-of-line copy ctors for complex classes.

printing/backend/print_backend.h

Index: printing/backend/print_backend.h
diff --git a/printing/backend/print_backend.h b/printing/backend/print_backend.h
index a8123325a613f527ba4e91a412ba09cd3225c8ec..621278bfc68bc0d3a5fd7847c5c55605cbfa7e42 100644
--- a/printing/backend/print_backend.h
+++ b/printing/backend/print_backend.h
@@ -23,6 +23,7 @@ namespace printing {
 
 struct PRINTING_EXPORT PrinterBasicInfo {
   PrinterBasicInfo();
+  PrinterBasicInfo(const PrinterBasicInfo& other);
   ~PrinterBasicInfo();
 
   std::string printer_name;
@@ -65,6 +66,7 @@ struct PRINTING_EXPORT PrinterSemanticCapsAndDefaults {
 
 struct PRINTING_EXPORT PrinterCapsAndDefaults {
   PrinterCapsAndDefaults();
+  PrinterCapsAndDefaults(const PrinterCapsAndDefaults& other);
   ~PrinterCapsAndDefaults();
 
   std::string printer_capabilities;