Note: We should verify that this works on a single device.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b08b2bd5ae5132ba7d06325cc158d9165611e1b9

commit b08b2bd5ae5132ba7d06325cc158d9165611e1b9
Author: Thanh Pham <thanhph@chromium.org>
Date: Tue Jul 11 04:23:22 2017

Use ui::layer for highlighting instead of widget.

Currently Devtools uses widget to highlight elements, i.e.,
windows, widgets, and views. We instead can ui::layer for highlighting
and to support future drawing/animation.

Bug:  730828 
Change-Id: Ic84a79c382e2e3a2bcf0b9cba421d2cb9a8e72bc
Reviewed-on: https://chromium-review.googlesource.com/564036
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485519}
[modify] https://crrev.com/b08b2bd5ae5132ba7d06325cc158d9165611e1b9/components/ui_devtools/views/ui_devtools_dom_agent.cc
[modify] https://crrev.com/b08b2bd5ae5132ba7d06325cc158d9165611e1b9/components/ui_devtools/views/ui_devtools_dom_agent.h
[modify] https://crrev.com/b08b2bd5ae5132ba7d06325cc158d9165611e1b9/components/ui_devtools/views/ui_devtools_unittest.cc
[modify] https://crrev.com/b08b2bd5ae5132ba7d06325cc158d9165611e1b9/components/ui_devtools/views/ui_element_delegate.h
[modify] https://crrev.com/b08b2bd5ae5132ba7d06325cc158d9165611e1b9/components/ui_devtools/views/window_element.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ca6bf7dec0d7bd9756d874b279bbb4644d33ecf2

commit ca6bf7dec0d7bd9756d874b279bbb4644d33ecf2
Author: Thanh Pham <thanhph@chromium.org>
Date: Wed Jul 12 04:17:33 2017

Rename highlight_window to root_window.

Bug:  730828 
Change-Id: Ibf29dfcac0180a1c5240e47ad59f6c6f6c9479de
Reviewed-on: https://chromium-review.googlesource.com/567703
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485849}
[modify] https://crrev.com/ca6bf7dec0d7bd9756d874b279bbb4644d33ecf2/components/ui_devtools/views/ui_devtools_unittest.cc

From sadrul@: this should now be fixed.