Read --dart-define in RendererBinding.initInstances()

[LongCatIsLooong]

Move SKPARAGRAPH_REMOVE_ROUNDING_HACK reading to the framework from dart:ui so flutter run --dart-define="SKPARAGRAPH_REMOVE_ROUNDING_HACK=false" works

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[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie on the #hackers channel in Chat (don't just cc him here, he won't see it! He's on Discord!).

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[Hixie]

doing it in a constructor seems like it would mean we're doing it more than once, when we only need to do it once, right? would the binding be a better place for it maybe?

[Hixie]

Can you leave a pointer to the documentation of what this is? Just so we can follow the breadcrumb trail if someone new needs to clean this up later.

[Hixie]