Added a webpack benchmark: the basic output of create-react-app.

[aickin]

This PR adds the unminified output of create-react-app as a benchmark script, as a good example of webpack output.

On master I get:

create-react-app.js: 29.91ms
create-react-app.optimized.js: 29.68ms
create-react-app.min.js: 20.87ms
create-react-app.min.optimized.js: 20.58ms

On aickin/optimize-js webpack-specific branch, I get:

create-react-app.js: 29.33ms
create-react-app.optimized.js: 6.47ms
create-react-app.min.js: 20.06ms
create-react-app.min.optimized.js: 6.63ms

One really bad thing about this PR is that the "Run all" button in the benchmark now consistently crashes Chrome for me part way through the benchmark. Each benchmark is still individually runnable, but if you try to run all of them, it crashes. I don't know what to do about that.

In case you want to re-create this file at some point, I did the following to generate the benchmark file:

• Used create-react-app to make a new project.
• npm run eject
• Removed UglifyPlugin from config/webpack.config.prod.js
• Modified src/index.js, removing the call ReactDOM.render and replacing it with:

window.React = React;
window.ReactDOM = ReactDOM;
window.app = <App />;

• npm run build
• Copy build/static/js/main.<hash>.js to this benchmark folder as create-react-app.js.
• Add the __start and __end benchmarking lines from the other benchmarks to the top and bottom of the file.

[nolanlawson]

I'm guessing Chrome crashes because of a memory leak, but I'm still happy to merge this because it looks like a great test case. Thank you!