originate(line, column, source) {
    line++;  // source map lib uses one-based lines.
    // Try to get a mapping for every input line.
    if (this.original_ && this.original_.line !== line)
      this.flushMappings();
    // The first mapping on each output line must cover beginning columns.
    this.original_ = {line, column};
    let {name} = source;
    if (name && !this.sourcesInMap_.has(name)) {
      this.sourcesInMap_.add(name);
      this.relativeSourceName_ = relativePath(name, this.basepath_);
      this.sourceMapGenerator_.setSourceContent(this.relativeSourceName_,
          source.contents);
    }
    this.flushMappings();
  }
Set the original coordinates for the generated position.
@param {number} line
@param {number} column
@param {SourceFile} source