The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3fee0191fca4632f7ddaed1b359da77543ab302a

commit 3fee0191fca4632f7ddaed1b359da77543ab302a
Author: Thanh Pham <thanhph@chromium.org>
Date: Sat Oct 07 00:22:57 2017

Show 2 rulers along top/left side whenever in inspect mode for UI
Devtools.

It's hard to use guide lines without rulers. This cl adds a top ruler
and a left ruler to help users locate and move UI Element along guide
lines.

Current ruler UI:
https://drive.google.com/open?id=0B0MnJn1TtqqtaC1sdzhUeHNMLUE

Bug:  760198 
Change-Id: I4300cc0d860041f115a42503ca2a6acc28bc8b91
Reviewed-on: https://chromium-review.googlesource.com/694242
Commit-Queue: Thanh Pham <thanhph@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#507239}
[modify] https://crrev.com/3fee0191fca4632f7ddaed1b359da77543ab302a/components/ui_devtools/views/ui_devtools_dom_agent.cc