I am new to the community. Will try to solve this issue. 
Just to be clear, we need to close the Apps tab when we click in the area other than application icons, right? (For example: in the screen shot attached, if we click anywhere other than webstore or videostream for google chromecast, the App tab should be closed)

Deleted: Screen Shot 2016-06-16 at 11.38.47 PM.png 220 KB

	Screen Shot 2016-06-16 at 11.38.47 PM.png 220 KB View Download

@sanilf1: This is for Mash/Mustash - a new experimental runtime mode for Chrome on ChromeOS. The "Hotlist-GoodFirstBug" label in this case means it's a good starter bug if you are starting to work on the Mustash project. 
If you are new to the Chromium community in general and just looking to get familiar with the Chromium codebase, this is not a great candidate. Sorry for the confusion. Perhaps I am misusing the label in the

We can make AppListPresenterDelegateMus use views::WindowManagerConnection::Get()->AddPointerWatcher() in order to implement this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e1490a565be9fb332dd94b7f65518ea36c8251bf

commit e1490a565be9fb332dd94b7f65518ea36c8251bf
Author: thanhph <thanhph@chromium.org>
Date: Fri Oct 21 22:09:30 2016

Mash: Close app list widget when users click outside of the widget

Use PointerWatcherEventRouter/ui::PointerEvent to detect when a user clicks outside the visible app-list widget,
and close it. Make sure the app list is dismissed if the presenter is destroyed while it is visible.

BUG= 611447 

Review-Url: https://chromiumcodereview.appspot.com/2434573004
Cr-Commit-Position: refs/heads/master@{#426909}

[modify] https://crrev.com/e1490a565be9fb332dd94b7f65518ea36c8251bf/chrome/browser/ui/ash/app_list/app_list_presenter_delegate_mus.cc
[modify] https://crrev.com/e1490a565be9fb332dd94b7f65518ea36c8251bf/chrome/browser/ui/ash/app_list/app_list_presenter_delegate_mus.h
[modify] https://crrev.com/e1490a565be9fb332dd94b7f65518ea36c8251bf/chrome/browser/ui/ash/app_list/app_list_service_ash.cc
[modify] https://crrev.com/e1490a565be9fb332dd94b7f65518ea36c8251bf/ui/app_list/presenter/app_list_presenter_impl.cc
[modify] https://crrev.com/e1490a565be9fb332dd94b7f65518ea36c8251bf/ui/app_list/presenter/app_list_presenter_impl.h