[win] Set the drag item visible when externally cancelling a drag in the app launcher

[win] Set the drag item visible when externally cancelling a drag in the app launcher

When the nested message loop running a synchronous drag event on windows
is cancelled due to an external event, it does not currently set the
item visible again.

Now it does.

BUG=393519
TEST=Open a signed-in profile on two computers. On one computer,
uninstall an app from the app launcher. Then, Quickly switch to the
other computer and start dragging around a different app. When the sync
event to uninstall the app comes in, the drag should cancel, with the
item being dragged reappearing.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=287499

[tapted, 2014-08-05 01:45:36]

ben likes synchronous drag CLs :)

Pretty sure this isn't one of those camel-breaking straw things -- tested all
the code paths with/without folders that I could think of, and eyeballed the
logic flow around this (i.e. none of the the codepaths leading up to that DCHECK
should cause it to ever fail).

[benwells, 2014-08-05 03:39:55]

lgtm

[tapted, 2014-08-05 03:51:21]

The CQ bit was checked by tapted@chromium.org

[commit-bot: I haz the power, 2014-08-05 03:53:16]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/tapted@chromium.org/435303005/1

[commit-bot: I haz the power, 2014-08-05 04:58:58]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  chromium_presubmit on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)
  linux_chromium_chromeos_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[commit-bot: I haz the power, 2014-08-05 08:27:43]

Change committed as 287499