constructor(
    map: MixedSourceMap,
    normalizeSourceFn: SourceNameNormalizer = normalizeSourcePath,
  ) {
    this._sourceMap = map;
    this._decodedFunctionMapCache = new Map();
    this._normalizeSource = normalizeSourceFn;
  }
Consumes the `x_facebook_sources` metadata field from a source map and
exposes various queries on it.

By default, source names are normalized using the same logic that the
`source-map@0.5.6` package uses internally. This is crucial for keeping the
sources list in sync with a `SourceMapConsumer` instance.
If you're using this with a different source map reader (e.g. one that
doesn't normalize source names at all), you can switch out the normalization
function in the constructor, e.g.

    new SourceMetadataMapConsumer(map, source => source) // Don't normalize