sourceFiles no longer added to program emit callback

[tlancina]

It looks like there was possibly a small regression in cfa4388, undoing part of #7525. It seems like there was a manual merge there as well, so it's hard to see what the actual changes were.

https://github.com/Microsoft/TypeScript/blob/877e3c48156619aa934c3188d39cf912eeba3b72/src/compiler/emitter.ts#L767

Related: #7438.

TypeScript Version: 2.1.1

Code

import * as ts from 'typescript';
const files = ['index.ts']
const program = ts.createProgram(files, {});
program.emit(undefined, (path: string, data: string, writeByteOrderMark: boolean, onError: Function, sourceFiles: ts.SourceFile[]) => {
  // prints undefined on 2.1.1, 1 on earlier versions
  console.log(sourceFiles && sourceFiles.length);
});

Expected behavior: sourceFiles are added to emit callback

Actual behavior: sourceFiles are undefined