The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5851f75e9af166477ceb75f3d51126c44dd77ead

commit 5851f75e9af166477ceb75f3d51126c44dd77ead
Author: Thanh Pham <thanhph@chromium.org>
Date: Tue Sep 12 01:39:18 2017

Use mousewheel to change the pinned node in UI DevTools.

When an element X is pinned in UI DevTools inspect mode, moving the
mouse cursor over X and scrolling the mousewheel up should change X to
be the parent of X. This will also show the distances between vertical
and horizontal distances between X and X's parent.

For now, make scrolling the mousewheel down a no-op; if the user wishes
to pin a child element of the currently-pinned element, this can be
accomplished with a click.

Bug:  748138 
Change-Id: I61ed0743d96f0021201e329d0c1d765a16004c0a
Reviewed-on: https://chromium-review.googlesource.com/594587
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Thanh Pham <thanhph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501143}
[modify] https://crrev.com/5851f75e9af166477ceb75f3d51126c44dd77ead/components/ui_devtools/views/ui_devtools_dom_agent.cc
[modify] https://crrev.com/5851f75e9af166477ceb75f3d51126c44dd77ead/components/ui_devtools/views/ui_devtools_dom_agent.h
[modify] https://crrev.com/5851f75e9af166477ceb75f3d51126c44dd77ead/components/ui_devtools/views/ui_devtools_overlay_agent.cc
[modify] https://crrev.com/5851f75e9af166477ceb75f3d51126c44dd77ead/components/ui_devtools/views/ui_devtools_overlay_agent.h
[modify] https://crrev.com/5851f75e9af166477ceb75f3d51126c44dd77ead/components/ui_devtools/views/ui_devtools_unittest.cc