Add const qualifier to ServiceWorkerFetchRequest::Serialize

Bug: N/A
Change-Id: I8874134483806c01323042ad7593125e1e2c7b35
Reviewed-on: https://chromium-review.googlesource.com/1059782Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Commit-Queue: Rayan Kanso <rayankans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558718}

content/common/service_worker/service_worker_types.cc

@@ -56,7 +56,7 @@ ServiceWorkerFetchRequest& ServiceWorkerFetchRequest::operator=(
 
 ServiceWorkerFetchRequest::~ServiceWorkerFetchRequest() {}
 
-std::string ServiceWorkerFetchRequest::Serialize() {
+std::string ServiceWorkerFetchRequest::Serialize() const {
   proto::internal::ServiceWorkerFetchRequest request_proto;
 
   request_proto.set_url(url.spec());

content/common/service_worker/service_worker_types.h

@@ -90,7 +90,7 @@ struct CONTENT_EXPORT ServiceWorkerFetchRequest {
   ServiceWorkerFetchRequest& operator=(const ServiceWorkerFetchRequest& other);
   ~ServiceWorkerFetchRequest();
   size_t EstimatedStructSize();
-  std::string Serialize();
+  std::string Serialize() const;
 
   static blink::mojom::FetchCacheMode GetCacheModeFromLoadFlags(int load_flags);
   static ServiceWorkerFetchRequest ParseFromString(