Fix bug 2495033.

AutoCompleteTextView now uses different logic to expand the dropdown
list of completion choices to cover the IME if present. Previously
this would happen whenever a touch down event occurred. Resizing the
dropdown could cause the parent view to animate a scroll and thereby
move the completion list up the screen. When this happened with a
finger down it would initiate a touch scroll on the completion
list. Prior to froyo this wasn't a problem since a list positioned at
the top could not scroll up, but with the addition of overscroll this
caused undesired behavior.

The completion list now will not expand to cover the IME on initial
touch down. Instead it will only expand if the user leaves a finger in
place for the duration of a timeout (currently 250ms) or if the user
explicitly begins a touch scroll on the completion list. This also has
a nice side effect where tapping a completion choice in the initial,
smaller list does not cause a split-second list expansion before the
list is dismissed.

Change-Id: If0994c68a91b3bfc3dcef660c67fde667a9727f9