Fix iOS builds: InlinedStructPtr is not copyable. Avoid the same while...

Fix iOS builds: InlinedStructPtr is not copyable. Avoid the same while iterating over request headers.

sky/services/ns_net/url_loader_impl.mm

@@ -133,7 +133,7 @@ void URLLoaderImpl::Start(URLRequestPtr request,
 
   req.HTTPMethod = @(request->method.data());
 
-  for (auto header : request->headers) {
+  for (const auto& header : request->headers) {
     NSString *name = @(header->name.data());
     NSString *value = @(header->value.data());
     [req addValue:value forHTTPHeaderField:name];