Open browser after devserver compilation

[darajava]

Is your proposal related to a problem?

When running npm run start, the browser opens almost immediately leaving a blank page for a good few seconds before the code is actually compiled.

Describe the solution you'd like

It would be better if the browser only gets invoked after compilation has passed.

Additional context

This can be achieved easily with WebpackDevServer hooks as with the following snippet:

let compiledOnce = false;
// After WebpackDevServer compiles the bundle, open it in the browser.
compiler.hooks.afterCompile.tap(appName, () => {
  if (!compiledOnce) {
    openBrowser(urls.localUrlForBrowser);
  }
  compiledOnce = true;
});

(Maybe someone can help me with that ugly boolean variable that is required to prevent new tabs when hot reloading)

[darajava]

I can't seem to create a PR for this, but it's ready to go in a branch if people think it's a good idea!

[darajava]

@gaearon