Returning a Promise from 'executeMainProcessMethod'

[magaya-dev]

In execute-js-func.js initializeEvalHandler uses a function executeMainProcessMethod which is not prepared to handle Promises. This causes issues when paired with createProxyForMainProcessModule and working with Promises. There is another method, evalRemoteMethod, which is prepared to handle Promises. Could both cases (calling a renderer and calling the main process) be made to work with Promises?

[queesamor]

I have the same issue. Pull request #30, when implemented manually, solves this for me. See my note here: https://github.com/electron-userland/electron-remote/pull/30#issuecomment-437711238