function runTasks(aTasks) {
			clearTimeout(iTimeoutId);
			while (aTasks.length) {
				aTasks.shift()();
			}
			if (that.aPrerenderingTasks === aTasks) {
				that.aPrerenderingTasks = null;
			}
		}
Adds a task that is guaranteed to run once, just before the next rendering without initiating
a rendering request. A watchdog ensures that the task is run soon, even if no rendering
occurs.

@param {function} fnPrerenderingTask
  A function that is called before the rendering
@param {boolean} [bFirst]
  Whether the task should become the first one, not the last one
@private