function compile(srcs, out, args) {
  // Get the compiler arguments, using the defaults if not specified.
  const combinedArgs = Object.assign({}, COMPILER_DEFAULT_ARGS, args);
  return gulp
      .src(srcs)
      .pipe(closureCompiler({
        compilerPath: COMPILER_PATH,
        fileName: path.basename(out),
        compilerFlags: combinedArgs
      }))
      .pipe(gulp.dest(path.dirname(out)));
}
Invokes Closure Compiler.
@param {!Array<string>} srcs The JS sources to compile.
@param {string} out The path to the output JS file.
@param {!Object} args Additional arguments to Closure compiler.
@return {*} A stream that finishes when compliation finishes.