ChooserActivity direct share jank fixes

Don't show the ChooserTargetService targets until we have all
responses in, or we hit our timeout. This helps prevent targets from
jumping around under the user's finger. We still give bonuses to
services that respond faster.

Bug 26790940

Change-Id: I8a19e19e08eeb502ccc4b4feaa1710ca3315e9f6