[webkit-dev] Adding high resolution platform timestamp to DOM events

[Robert Flack]

Hi webkit-dev,

I would like to add platform timestamps to DOM events as the systemTime
property. I have a patch implementing the feature:
https://bugs.webkit.org/show_bug.cgi?id=94987. This will let us know the
time at which the system received an event to be able to accurately handle
it, whereas the timestamp property gives the time the DOM event was created
in an inaccurate milliseconds since 1970 form. This has been discussed on
www-dom (http://lists.w3.org/Archives/Public/www-dom/2012OctDec/0028.html)
and www-perf (
http://lists.w3.org/Archives/Public/public-web-perf/2012Oct/0046.html) and
use cases for this have been discussed (
http://lists.w3.org/Archives/Public/www-dom/2012AprJun/0092.html).

The platform timestamp comes in as a monotonic timestamp. Since the DOM
Event spec requires that timeStamp() be a 1970-epoch based timestamp it is
not sufficient for a high resolution precise time delta on event delivery.
Instead, we add a systemTime property which uses the Performance API spec (
http://dvcs.w3.org/hg/webperf/raw-file/tip/specs/HighResolutionTime/Overview.html)
for high res timestamps (time since document load timestamp to avoid user
fingerprinting) and provide the platform's high resolution timestamp to
ECMAScript.

Let me know if you have any suggestions. I look forward to everyone's
feedback, cheers!
- Rob
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