e.g. the accessibility system contains at least two uses of WTF::String::SimplifyWhiteSpace which do not use the result. This method, like many others, does not modify the string but returns a new string with the modification applied.

At the moment, these call sites are no-ops, but they may be bugs. Someone should audit such call sites, remove or fix them, and then add WARN_UNUSED_RESULT to the member functions to prevent this sort of issue in the future.