Changes layer reparenting to happen after a window parent is changed in aura::Window::AddChild

Changes layer reparenting to happen after a window parent is changed in aura::Window::AddChild

BUG=364498
TEST=Follow steps in the bug or at https://code.google.com/p/chromium/issues/detail?id=364517. Ensure no crash.
TEST=aura_unittests --gtest_filter=WindowTest.RootWindowSetWhenReparenting

This addresses a class of crashes that happen when layers bounds are updated while the code is in child->ReparentLayers inside Window::AddChild where the window is removed from its old parent but not yet added to the new parent. GetRootWindow would return NULL causing crashes in places where we assume that (Window::IsVisible() == (Window::GetRootWindow() != NULL)).
There was a discussion about windows that are detached from the root - see here - https://codereview.chromium.org/82283002#msg12. It looks like the result of that discussion was that we should fix places where we assume that IsVisible() == (Window::GetRootWindow() != NULL). VideoDetector::MaybeNotifyObservers is one such place, NativeWidgetAura::IsMouseEventsEnabled() is another such place, there are probably many more.

This CL tries to avoid this whole class of errors by restoring the sequence in AddChild that existed before https://codereview.chromium.org/82283002.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=265565

[varkha, 2014-04-17 18:10:20]

sky@, can you please comment on this? Can you think of anything that this change
would break? Thanks!

[varkha, 2014-04-17 18:14:00]

Those are two crashes that I have found so far that should be fixed with this:
https://crash.corp.google.com/samples?stbtiq=328f9b79da4daa03#4.
https://crash.corp.google.com/samples?stbtiq=f76689467f76ba90#4.

[sky, 2014-04-17 21:56:49]

This seems fine. But update your description (since it isn't a hack) and add
test coverage.

[varkha, 2014-04-22 18:30:17]

PTAL. I have added a test to verify that the root window is not lost during
reparenting.

[sky, 2014-04-22 19:43:23]

LGTM

[varkha, 2014-04-22 19:44:49]

The CQ bit was checked by varkha@chromium.org

[commit-bot: I haz the power, 2014-04-22 19:45:28]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/varkha@chromium.org/241243002/20001

[commit-bot: I haz the power, 2014-04-22 20:51:35]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-04-22 20:51:36]

Try jobs failed on following builders:
  tryserver.chromium on win_chromium_rel

[varkha, 2014-04-22 21:01:16]

The CQ bit was checked by varkha@chromium.org

[commit-bot: I haz the power, 2014-04-22 21:04:41]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/varkha@chromium.org/241243002/20001

[commit-bot: I haz the power, 2014-04-22 21:10:02]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-04-22 21:10:02]

Try jobs failed on following builders:
  tryserver.chromium on win_chromium_x64_rel

[varkha, 2014-04-22 21:11:00]

The CQ bit was checked by varkha@chromium.org

[commit-bot: I haz the power, 2014-04-22 21:11:39]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/varkha@chromium.org/241243002/20001

[varkha, 2014-04-22 23:43:43]

The CQ bit was unchecked by varkha@chromium.org

[varkha, 2014-04-23 02:47:03]

sky@, could you please look at this again? I thought it would be more correct to
call GetAncestorWithLayer before setting a new parent since it should not use
parent to calculate offset. This reduces the scope of the change. Thanks.

[sky, 2014-04-23 02:55:13]

Did you upload a new patchset?

[varkha, 2014-04-23 03:24:15]

On 2014/04/23 02:55:13, sky wrote:
> Did you upload a new patchset?

Yes I did. The only difference (please ignore the rebase) is in where the new
parent is established (after a call to GetAncestorWithLayer).
https://codereview.chromium.org/241243002/diff2/20001:40001/ui/aura/window.cc

[sky, 2014-04-23 04:55:25]

SLGTM

[varkha, 2014-04-23 05:05:07]

The CQ bit was checked by varkha@chromium.org

[commit-bot: I haz the power, 2014-04-23 05:05:34]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/varkha@chromium.org/241243002/40001

[commit-bot: I haz the power, 2014-04-23 08:09:13]

Change committed as 265565