Select the pointed item when drag operation starts.

Select the pointed item when drag operation starts.

What this CL do:
 If there is an item at the drag's starting position and
the item is not selected, select the item.

Why this handling is needed:
 If the drag operation is initiated by mouse, the
'mousedown' event eventually selects the pointed item,
but there is no such chance when the drag operation is 
initiated by touch.

BUG=373839
TEST=manually tested

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=271535

[fukino, 2014-05-19 11:24:32]

Hi @arv,
I'd like to add one more handling for touch operation in the cr.ui.List.
This is for Drag&Drop.
When Drag&Drop is initiated by touch operation, a list item under the finger is
not necessarily dragged, and this CL is intended to fix this issue. 
Could you take a look?

[arv (Not doing code reviews), 2014-05-19 18:14:10]

Why isn't the item selected before the dragstart event? Is it because we are not
sending the expected events?

[fukino, 2014-05-19 23:42:18]

On 2014/05/19 18:14:10, arv wrote:
> Why isn't the item selected before the dragstart event? Is it because we are
not
> sending the expected events?

The item would be selected if mousedown event was sent before dragstart,
but mousedown is sent with touchend.
I think it is expected according to the default action of "5.4 List of
TouchEvent types" in http://www.w3.org/TR/touch-events/ .

Another candidate timing to select the item is touchstart.
But we should not select the item when we want to scroll the list, so we can't
select the item in touchstart.

So, I think dragstart is the best timing to select the item in touch operation.

[arv (Not doing code reviews), 2014-05-20 00:31:30]

LGTM

Thanks for explaining.

[fukino, 2014-05-20 00:39:19]

The CQ bit was checked by fukino@chromium.org

[commit-bot: I haz the power, 2014-05-20 00:40:49]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/fukino@chromium.org/288883004/1

[commit-bot: I haz the power, 2014-05-20 02:07:25]

Change committed as 271535