chore: disable Puppeteer default viewport to increase its size (#947)

According to [Puppeteer documentation for launch options](https://github.com/GoogleChrome/puppeteer/blob/v1.14.0/docs/api.md#puppeteerlaunchoptions), setting `defaultViewport` to `null` disables the default viewport size of 800x600. When the default viewport is disabled, the viewport size matches the browser size. This makes failture screenshots more meaningful when debugging flaky E2E tests because they will show more than the top left portion of the page that is being tested.

Author: lisli1

src/tests/end-to-end/common/browser-factory.ts

@@ -61,6 +61,7 @@ async function launchNewBrowser(): Promise<Puppeteer.Browser> {
     const browser = await Puppeteer.launch({
         // Headless doesn't support extensions, see https://github.com/GoogleChrome/puppeteer/issues/659
         headless: false,
+        defaultViewport: null,
         args: [
             // Required to work around https://github.com/GoogleChrome/puppeteer/pull/774
             `--disable-extensions-except=${extensionPath}`,