grid loading animation performance impact

<zk>
	<zscript><![CDATA[
		ListModelList model = new ListModelList(Collections.nCopies(1000, "dummy"));
	]]></zscript>
	<grid model="${model}" height="700px" style="background:#ddd">
		<custom-attributes org.zkoss.zul.grid.rod="true"/>
		<template name="model">
			<row>
				<cell>Cell</cell>
				<cell>Cell</cell>
				<cell>Cell</cell>
			</row>
		</template>
	</grid>
</zk>

When ROD is enabled, the data loading indicator animation ZK-3138 causes constant CPU load and should only be displayed if necessary
(even if off screen animations may cause CPU load especially in IE)

The effect is worse when using iceblue theme, since the gif animation has a higher frequency.

Having multiple grids on a page accumulates the effect as well.

When disabling ROD the CPU usages is 0%. as expected