Merge pull request #215 from android/update-agp-4-2-1

[StylianosGakis]

Fix DiffUtil.ItemCallback implementation

The areItemsTheSame documentation explicitly says:
"For example, if your items have unique ids, this method should check their id equality."

In the current state, the DiffUtil.ItemCallback is implemented wrong.

views-widgets-samples/RecyclerViewKotlin/app/src/main/java/com/example/recyclersample/flowerList/FlowersAdapter.kt

Lines 77 to 83 in f22069a

	override fun areItemsTheSame(oldItem: Flower, newItem: Flower): Boolean {
	return oldItem == newItem
	}
	override fun areContentsTheSame(oldItem: Flower, newItem: Flower): Boolean {
	return oldItem.id == newItem.id
	}