src/closure-compiler-plugin.js
function findChunkFile(chunk, chunkId, outputFilePath) {
  for (let i = 0; i < chunk.files.length; i++) {
    const chunkFile = chunk.files[i];
    let normalizedOutputFilePath = outputFilePath.replace(/^\.\//, '');
    if (!/\.js$/.test(chunkFile)) {
      normalizedOutputFilePath = normalizedOutputFilePath.substr(
        0,
        normalizedOutputFilePath.length - 3
      );
    }

    if (normalizedOutputFilePath === chunkFile) {
      return chunkFile;
    }
  }
  if (chunk.id === chunkId) {
    return chunk.files[0];
  }
  return undefined; // eslint-disable-line no-undefined
}
function findChunkFile(chunk, chunkId, outputFilePath) {
  for (let i = 0; i < chunk.files.length; i++) {
    const chunkFile = chunk.files[i];
    let normalizedOutputFilePath = outputFilePath.replace(/^\.\//, '');
    if (!/\.js$/.test(chunkFile)) {
      normalizedOutputFilePath = normalizedOutputFilePath.substr(
        0,
        normalizedOutputFilePath.length - 3
      );
    }

    if (normalizedOutputFilePath === chunkFile) {
      return chunkFile;
    }
  }
  if (chunk.id === chunkId) {
    return chunk.files[0];
  }
  return undefined; // eslint-disable-line no-undefined
}
Find the filename of a chunk which matches either the id or path provided.

@param {!Chunk} chunk
@param {number} chunkId
@param {string} outputFilePath
@return {string|undefined}