Mirror Safari iOS for MessagePort worker support

[autonome]

Summary

It's likely that iOS should mirror desktop here, but need to verify.

Test results and supporting details

Can't find anything in release notes yet.

[caugner]

I'm wondering if @queengooborg might have come across evidence to intentionally set Safari iOS to 5 in this commit.

Otherwise MessagePort was implemented in WebKit/WebKit@42ae99f, i.e. 533.9 before Safari Desktop 5 (533.16), and technically also before Safari iOS 4.2 (533.17), which explains the support statement of the parent feature.

The commit message mentions this:

Added a MessagePort implementation. Currently, it is not thread-safe at all, and only works with Documents as contexts, but in the future, it will be used for communication with worker threads.

But I found WebKit/WebKit@e573a5a mentioning "Implement Worker messaging" and WebKit/WebKit@5dcde16 mentioning "support for multi-threaded MessagePorts" in the same WebKit version.

So it's plausible that worker support landed in Safari 5 and Safari iOS 4.2.

[caugner]

Looking at https://developer.mozilla.org/en-US/docs/Web/API/Worker#browser_compatibility, it might be that worker support only landed in Safari on iOS 5, and not yet in Safari 4.2. Or that version is wrong as well.

Edit: The original data for Worker support was added in f09df1e (with Safari in iOS 5.1), but the PR seems to be based on the MDN page at the time that indicated these versions, and does not provide further evidence.