Skip over playback gaps that occur in the beginning of streams

[evanfarina]

Description

Fixes #1084 . There is an edge case that is exposed when a gap exists at the beginning of the stream and no content is buffered by the time the first waiting event has emitted. This leaves the player in a state where it's no longer checking for playback stalls (or gaps).

Specific Changes proposed

As mentioned in the linked issue, we have decided to proceed by checking for stalls when the first play event is emitted.

Requirements Checklist

• [ x] Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • [ x] Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors

[gesinger]

Thank you for the PR! A few minor comments.

[gesinger]

All the changes look good, thank you @evanfarina , but one thing I noticed during testing is that if you're using the test page with autoplay on and load the source again (the test source you provided in the issue) instead of refreshing the page, it won't skip the gap the second time. I don't think this should block us from pushing this PR through, but if you wanted to take a look at how source setting behavior might impact things, and if this will still be an issue for your use-case, we can either do it here, have another PR, or create a separate issue and handle it later.

[welcome]

Congrats on merging your first pull request! 🎉🎉🎉