Stopwatch should use window.performance.now if available

[jmesserly]

From the mailing list:

Just looking at code using Stopwatch and noticed it doesn't use window.performance.now if it's available. Couldn't find an issue for it so thought to ask what people's thoughts were regarding its use? (hoping for a one-off test rather than a per-use test)

Reference:
http://updates.html5rocks.com/2012/05/requestAnimationFrame-API-now-with-sub-millisecond-precision

jmesserly: this should give precision on the VM (because it uses Clock), but dart2js Clock uses JS Date.now(), which I think is only millisecond precision.

[kasperl]

Removed Area-Dart2JS label.
Added Area-Library label.

[sethladd]

See also issue #1881

[sethladd]

Moving this to Area-HTML because it's specifically talking about HTML implementation of stopwatch.

This would be a nice change.

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cc @rakudrama.
Removed Type-Defect, Area-Library labels.
Added Type-Enhancement, Area-HTML labels.

[vsmenon]

Added this to the M2 milestone.

[efortuna]

From what I can tell, there is no HTML-specific implementation of stopwatch

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Set owner to @efortuna.

[efortuna]

Fixed in r 15343 with CL: https://codereview.chromium.org//11417110

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Added Fixed label.