[WIP] make GURL::path() return a StringPiece

ios/web/public/test/response_providers/file_based_response_provider_impl.mm

Index: ios/web/public/test/response_providers/file_based_response_provider_impl.mm
diff --git a/ios/web/public/test/response_providers/file_based_response_provider_impl.mm b/ios/web/public/test/response_providers/file_based_response_provider_impl.mm
index d7740b2caeda7a38c9b256d568a0be2dc2072d4a..0f3152bffb8fd51707bd3a79f987b532c4199c15 100644
--- a/ios/web/public/test/response_providers/file_based_response_provider_impl.mm
+++ b/ios/web/public/test/response_providers/file_based_response_provider_impl.mm
@@ -27,7 +27,7 @@ base::FilePath FileBasedResponseProviderImpl::BuildTargetPath(const GURL& url) {
   if (url.host() != kLocalhostHost) {
     result = result.Append(url.host());
   }
-  std::string url_path = url.path();
+  std::string url_path = url.path().as_string();
   // Remove the leading slash in url path.
   if (url_path.length() > 0 && url_path[0] == '/') {
     url_path.erase(0, 1);