David Taylor 4d3eb3f1ac
PERF: Set --header-offset property only when changed (#15107)
Calling `setProperty("--header-offset", newValue)` will always cause a 'Recalculate Style' event, even if the value is unchanged. On my browser, these 'Recalculate Style' events take about 6-7ms each time the `dockCheck` function is run.

This commit stores the 'previous' value in an instance variable, and only calls setProperty if the value has changed. This brings the total runtime of `dockCheck` down to about 70µs on my machine.
2021-11-26 15:25:03 +00:00
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