Add support for shared workers

[stutrek]

Title sums it up. This adds support for SharedWorker. The API is the same. Tests were added too.

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[stutrek]

@googlebot I signed it!

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CLAs look good, thanks!

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[stutrek]

@developit any chance you could take a look? Thanks.

[lasseborly]

This would be great to have merged @developit 👍

[skmvasu]

Any plans to merge this? @developit Happy to help incase there is an issue and needs to be fixed. This will help us out in a few projects

[developit]

Looks great! Sorry I took so long to merge your PR!