Added Library-Isolate label.

Removed Library-Isolates label.

I don't think we should reduce the precision of timers on other platforms to match the limits of browser timers.

The problem with faster timers in browsers, as I understand it, was that JS programmers used zero-duration timer in order to get a timer callback "as fast as possible", but their code wasn't really build to work with <=1ms intervals, and it caused unnecessarily large power consumption on existing pages.

Dart code is unlikely to use that approach, since we have better primitives (like microtasks) and perhaps even timers that are already faster than 4ms in Dartium.

We can't document what the timer granularity is in general. It depends on the platform that Dart is running on, and how it's configured (high-resolution timers may be a system-wide setting).

So, no to to Timer restricting itself to existing browser JS behavior.
For documentation, the best we can say is that the granularity depends on the platform, system and configuration it's running on - which is really nothing.
We do write "Note: If Dart code using Timer is compiled to JavaScript, the finest granularity available in the browser is 4 milliseconds.".
I think we'll keep it at that.

Added NotPlanned label.