Cleanup return values in chrome/browser/ui/passwords

This CL turns const by value return values into const by ref.

Replacing const value by a const ref when a member variable is returned is safe, because the member variable will live at least as long as the temporary object returned now. It can also be more efficient, because returning a ref can spare copying.

BUG=393155

Review URL: https://codereview.chromium.org/416373002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@285588 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/ui/passwords/manage_passwords_ui_controller.h

@@ -94,7 +94,7 @@ class ManagePasswordsUIController
   // or not to save it.
   bool PasswordPendingUserDecision() const;
 
-  const autofill::ConstPasswordFormMap best_matches() const {
+  const autofill::ConstPasswordFormMap& best_matches() const {
     return password_form_map_;
   }