doc: add flag params (#132485)

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packages/flutter_tools/bin/xcode_debug.js

@@ -194,6 +194,7 @@ class CommandArguments {
    * return true. If the flag is not allowed for the current command, will
    * return `null`.
    *
+   * @param {!string} flag
    * @param {?string} value
    * @returns {?boolean}
    * @throws Will throw an error if the flag is allowed and `value` is not