[Identity] Use const ref on ExtensionTokenKey parameter

chrome/browser/extensions/api/identity/extension_token_key.cc

Index: chrome/browser/extensions/api/identity/extension_token_key.cc
diff --git a/chrome/browser/extensions/api/identity/extension_token_key.cc b/chrome/browser/extensions/api/identity/extension_token_key.cc
index 81329835a709e755ffeb48c0efdec5e9faf86485..146fc506d8919267b719ffdd297a445f2b693a44 100644
--- a/chrome/browser/extensions/api/identity/extension_token_key.cc
+++ b/chrome/browser/extensions/api/identity/extension_token_key.cc
@@ -8,7 +8,7 @@ namespace extensions {
 
 ExtensionTokenKey::ExtensionTokenKey(const std::string& extension_id,
                                      const std::string& account_id,
-                                     const std::set<std::string> scopes)
+                                     const std::set<std::string>& scopes)
     : extension_id(extension_id), account_id(account_id), scopes(scopes) {}
 
 ExtensionTokenKey::~ExtensionTokenKey() {}