def has_source_map?
      return false unless extname.downcase == '.js'
      lines.last(2).any? { |line| line.start_with?('//# sourceMappingURL') }
    end
def has_source_map?
      return false unless extname.downcase == '.js'
      lines.last(2).any? { |line| line.start_with?('//# sourceMappingURL') }
    end
Internal: Does the blob contain a source map reference?

 We assume that if one of the last 2 lines starts with a source map
 reference, then the current file was generated from other files.

 We use the last 2 lines because the last line might be empty.

 We only handle JavaScript, no CSS support yet.

 Returns true or false.