This patch:
- split browser launching logic from Browser into `lib/Launcher.js`
- introduce `puppeteer` namespace which currently has a single `launch`
method to start a browser
With this patch, the browser is no longer created with the `new
Browser(..)` command. Instead, it should be "launched" via the
`puppeteer.launch` method:
```js
const puppeteer = require('puppeteer');
puppeteer.launch().then(async browser => {
...
});
```
With this approach browser instance lifetime matches the lifetime of
actual browser process. This helps us:
- remove proxy streams, e.g. browser.stderr and browser.stdout
- cleanup browser class and make it possible to connect to remote
browser
- introduce events on the browser instance, e.g. 'page' event. In case
of lazy-launching browser, we should've launch browser when an event
listener is added, which is unneded comlpexity.
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