SomethingLikeThis.h

void
AssertAndSuppressCleanupFunc(ErrorResult* aRv)
{
  aRv->AssertReportedOrSuppressed();
  aRv->SuppressException();
}

template <typename CleanupFunc = AssertAndSuppressCleanupFunc>
class ErrorResult
{
  ~ErrorResult()
  {
    CleanupFunc(this);
  }
  
  ErrorResult<AssertAndSuppressCleanupFunc>& operator()
  {
    return *reinterpret_cast<ErrorResult<AssertAndSuppressCleanupFunc>*>(this);
  }
};

function SuppressCleanupFunc(ErrorResult* aRv)
{
  aRv->SuppressException();
}

typedef ErrorResult<SuppressCleanupFunc> IgnoredErrorResult;

function EmptyCleanupFunc(ErrorResult* aRv)
{
}

typedef ErrorResult<EmptyCleanupFunc> FastErrorResult;