If you want to use the new JavaScript for automation on Yosemite, you can display a scripts progress using a scripts Progress object.

ScriptProgressYosemite.js

Progress.totalUnitCount = 100
Progress.completedUnitCount = 0
Progress.description = "Testing progress"
Progress.additionalDescription = "foobar"

for(i = 0; i < Progress.totalUnitCount; i++) {
	Progress.description = "Item " + i + " of " + Progress.totalUnitCount
	delay(1)
	Progress.completedUnitCount = i
}