Resolve issues reported by Lighthouse

[joeyparrish]

Lighthouse reports the following issues with the Shaka Player demo:

• Manifest does not have icons at least 512px.
• First meaningful paint: 3,180 ms
• Perceptual Speed Index: 4,532 (target: < 1,250)
  • Reduce render-blocking scripts (these contribute 600 ms to load time)
  • Reduce render-blocking stylesheets (these contribute 590 ms to load time)
• Low contrast elements:
  • <a href="../docs/api/index.html">
  • <a href="https://github.com/google/shaka-player">
  • <a href="https://www.npmjs.com/package/shaka-player">
  • <a href="https://cdnjs.com/libraries/shaka-player">
  • <button id="loadButton">
• [user-scalable="no"] is not used in the element and the [maximum-scale] attribute is not less than 5.
  • Disabling zooming is problematic for users with low vision who rely on screen magnification to properly see the contents of a web page.
  • Failing element: <meta name="viewport" content="width=device-width, user-scalable=yes, initial-scale=1, maximum-scale=1">
• Does not use passive listeners to improve scrolling performance.

[joeyparrish]

Improvements after fixing render-blocking scripts:

• First meaningful paint: 660 ms
• Perceptual Speed Index: 1,982 (target: < 1,250)

[joeyparrish]

All touch event listeners are now marked explicitly with passive: false or passive: true. This does not silence the warning from Lighthouse, though, since one of them is still non-passive. It must remain so, since we call preventDefault() on the event.

Issues have already been filed on both Chrome and Lighthouse to fix this and respect passive: false:

• https://bugs.chromium.org/p/chromium/issues/detail?id=770208
• "Uses passive event listeners to improve scrolling performance" documentation needs updating GoogleChrome/lighthouse#3137

[joeyparrish]

The only remaining complaint from LightHouse is this one:

• Reduce render-blocking stylesheets (these contribute 590 ms to load time)

This is caused by Google Web Fonts, which seem fundamentally at odds with best practices recommended by Lighthouse. We will continue to use these fonts.