Update the comments related to the host window in SelectFileDialogImplGTK

Update the comments related to the host window in SelectFileDialogImplGTK

The comments need to be updated due to following reasons:
1. The bug mentioned in the comment cannot be reproducible.
   http://crbug.com/29213
2. AllBrowsersClosed() method was removed in the below CL, but
   it is still mentioned.
   https://codereview.chromium.org/231733005
3. The second case that |parent| is null is obsolete.

BUG=None

Committed: https://crrev.com/88ab2806cb68a0d3013ab7f9a215145e3ab1ee68
Cr-Commit-Position: refs/heads/master@{#388952}

[joone, 2016-04-21 21:59:26]

joone.hur@intel.com changed reviewers:
+ erg@chromium.org

[joone, 2016-04-21 21:59:27]

Hi erg@, can you take a look at this CL?

[Elliot Glaysher, 2016-04-21 22:24:41]

lgtm

[joone, 2016-04-21 22:26:05]

The CQ bit was checked by joone.hur@intel.com

[commit-bot: I haz the power, 2016-04-21 22:26:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1912873002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1912873002/1

[commit-bot: I haz the power, 2016-04-21 23:39:16]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-04-22 19:41:36]

Description was changed from

==========
Update the comments related to the host window in SelectFileDialogImplGTK

The comments need to be updated due to following reasons:
1. The bug mentioned in the comment cannot be reproducible.
   http://crbug.com/29213
2. AllBrowsersClosed() method was removed in the below CL, but
   it is still mentioned.
   https://codereview.chromium.org/231733005
3. The second case that |parent| is null is obsolete.

BUG=None
==========

to

==========
Update the comments related to the host window in SelectFileDialogImplGTK

The comments need to be updated due to following reasons:
1. The bug mentioned in the comment cannot be reproducible.
   http://crbug.com/29213
2. AllBrowsersClosed() method was removed in the below CL, but
   it is still mentioned.
   https://codereview.chromium.org/231733005
3. The second case that |parent| is null is obsolete.

BUG=None

Committed: https://crrev.com/88ab2806cb68a0d3013ab7f9a215145e3ab1ee68
Cr-Commit-Position: refs/heads/master@{#388952}
==========

[commit-bot: I haz the power, 2016-04-22 19:41:37]

Patchset 1 (id:??) landed as
https://crrev.com/88ab2806cb68a0d3013ab7f9a215145e3ab1ee68
Cr-Commit-Position: refs/heads/master@{#388952}