refactor: fix modernize-return-braced-init-list warnings (#44838)

* refactor: avoid repeating the return type from the declaration; use a braced initializer list instead [modernize-return-braced-init-list]

* refactor: avoid repeating the return type from the declaration; use a braced initializer list instead [modernize-return-braced-init-list]

NB: using the braced-initializer list uncovered an error here:
the float returned by std::floor() can't be implicitly cast to
an int. This is solved by using base::ClampFloor<int>() instead.
std::floor()

shell/browser/api/electron_api_crash_reporter.cc

@@ -99,7 +99,7 @@ std::string ReadClientId() {
   if (GetClientIdPath(&client_id_path) &&
       (!base::ReadFileToStringWithMaxSize(client_id_path, &client_id, 36) ||
        client_id.size() != 36))
-    return std::string();
+    return {};
   return client_id;
 }