Cleanup: Pass std::string as const reference if possible

components/network_hints/renderer/dns_prefetch_queue.h

Index: components/network_hints/renderer/dns_prefetch_queue.h
diff --git a/components/network_hints/renderer/dns_prefetch_queue.h b/components/network_hints/renderer/dns_prefetch_queue.h
index 72b4fadf162d1fb4e7507df3bd21d8cad5c7c816..7f5ac2f27e6f318521d6619e451226cedfdb7b9c 100644
--- a/components/network_hints/renderer/dns_prefetch_queue.h
+++ b/components/network_hints/renderer/dns_prefetch_queue.h
@@ -63,7 +63,7 @@ class DnsQueue {
   // Returns true for success, false for failure (nothing written).
   PushResult Push(const char* source, const size_t length);
 
-  PushResult Push(std::string source) {
+  PushResult Push(const std::string& source) {
     return Push(source.c_str(), source.length());
   }