Fix app list DCHECKs getting hit when model updates occur during dragging

Fix app list DCHECKs getting hit when model updates occur during dragging

The DCHECK from AppsGridView::UpdateDragFromItem() is changed
to an early return. This is a valid codepath, because drag events
can still arrive from the AppListItemView after a drag is cancelled,
e.g., via Sync.

AppsGridViewTest.MouseDragWithFolderDisabled is updated to
include coverage for this codepath.

A DCHECK was also hit in UpdateDragFromReparentItem(). This was not
a valid code path. The problem was that the root grid view tried
to cancel only its "part" of the drag, rather than forwarding the
cancel request to the folder managing the drag.

AppListMainViewTest.MouseDragItemOutOfFolderWithCancel is added to
include coverage for this codepath.

BUG=402784
TEST=app_list_unittests

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=289525

[tapted, 2014-08-12 06:51:55]

Hi Chris - PTAL. More analysis on the bug.

[tapted, 2014-08-12 07:17:54]

ugh - there's more of these. let me add more tests

[22048:22048:0812/171504:FATAL:apps_grid_view.cc(802)] Check failed: drag_view_.

#0 0x7fa1ba8a8d8e base::debug::StackTrace::StackTrace()
#1 0x7fa1ba93a825 logging::LogMessage::~LogMessage()
#2 0x7fa1b9368603 app_list::AppsGridView::UpdateDragFromReparentItem()

[tapted, 2014-08-13 06:44:30]

OK Chris - it's ready for you!

[calamity, 2014-08-14 01:22:04]

lgtm.

https://codereview.chromium.org/466693002/diff/80001/ui/app_list/views/app_li...
File ui/app_list/views/app_list_main_view_unittest.cc (right):

https://codereview.chromium.org/466693002/diff/80001/ui/app_list/views/app_li...
ui/app_list/views/app_list_main_view_unittest.cc:289:
TEST_F(AppListMainViewTest, MouseDragItemOutOfFolderWithCancel) {
nit: Test could use a comment.

[tapted, 2014-08-14 01:35:38]

https://codereview.chromium.org/466693002/diff/80001/ui/app_list/views/app_li...
File ui/app_list/views/app_list_main_view_unittest.cc (right):

https://codereview.chromium.org/466693002/diff/80001/ui/app_list/views/app_li...
ui/app_list/views/app_list_main_view_unittest.cc:289:
TEST_F(AppListMainViewTest, MouseDragItemOutOfFolderWithCancel) {
On 2014/08/14 01:22:04, calamity wrote:
> nit: Test could use a comment.

Done.

[tapted, 2014-08-14 01:35:58]

The CQ bit was checked by tapted@chromium.org

[commit-bot: I haz the power, 2014-08-14 01:37:35]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/tapted@chromium.org/466693002/100001

[commit-bot: I haz the power, 2014-08-14 07:44:51]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  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, 2014-08-14 11:22:00]

Committed patchset #5 (100001) as 289525