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

components/storage_monitor/storage_info.cc

Index: components/storage_monitor/storage_info.cc
diff --git a/components/storage_monitor/storage_info.cc b/components/storage_monitor/storage_info.cc
index 98bc7ce856b8de8622c81992683da28f22189796..a03394057efc88db7412d08fca7b967ace42bbf8 100644
--- a/components/storage_monitor/storage_info.cc
+++ b/components/storage_monitor/storage_info.cc
@@ -55,6 +55,8 @@ namespace storage_monitor {
 StorageInfo::StorageInfo() : total_size_in_bytes_(0) {
 }
 
+StorageInfo::StorageInfo(const StorageInfo& other) = default;
+
 StorageInfo::StorageInfo(const std::string& device_id_in,
                          const base::FilePath::StringType& device_location,
                          const base::string16& label,