Using the per-revision bisect providing the bisect results,
Good build: 56.0.2913.0 (Revision: 430459).
Bad build: 56.0.2914.0 (Revision: 430837).

You are probably looking for a change made after 430713 (known good), but no later than 430714 (first known bad).
CHANGELOG URL:
  https://chromium.googlesource.com/chromium/src/+log/2c944c9e76acc4e22a67bff89e33afd2342db0a1..cec7d0e095a1fb1304b6bda02129ac4cc117f134

@lushnikov -- Could you please look into the issue, pardon me if it has nothing to do with your changes and if possible please assign it to concern owner.

Thank You.

Adding release block label, please undo if not the case.

I've a workaround for this, now I'm just working out the root cause. May I take this issue for my first bug?

#3: Please, go ahead!

Able to reproduce the issue on windows 7 using chrome version 57.0.2952.0.
Any update on this issue please 

Thanks,

Please see https://codereview.chromium.org/2600493002/ :)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4d2364eb32a5b242790324536efccd843cb81aa8

commit 4d2364eb32a5b242790324536efccd843cb81aa8
Author: me <me@jakehendy.com>
Date: Mon Jan 23 08:29:15 2017

DevTools: Correct Source Panel Show/Hide Toolbar buttons

Regression : Misalignment of 'Hide Navigator' and 'Hide Debugger' buttons is seen in devtools.

Flipped mask positions and removed—now unnecessary—rotation transforms around show/hide panel icon containers.

BUG= 671930 
R=lushnikov@chromium.org
TEST=Open Dev Tools, open Sources Pane, observe show/hide sidebar buttons
are correctly aligned.  crbug.com/671930 

Review-Url: https://codereview.chromium.org/2600493002
Cr-Commit-Position: refs/heads/master@{#445339}

[modify] https://crrev.com/4d2364eb32a5b242790324536efccd843cb81aa8/AUTHORS
[modify] https://crrev.com/4d2364eb32a5b242790324536efccd843cb81aa8/third_party/WebKit/Source/devtools/front_end/ui/Icon.js

The solution turned out to be not working. I'm reverting the CL: 
https://codereview.chromium.org/2655793003/

The reason - the icons turned out to be different.
- Before patch: http://imgur.com/a/eFCnz
- After patch: http://imgur.com/a/gJ24q

Jake, would you like to give this another shot?

@lushnikov I knew there must have been a reason for the transforms in the first place!

If I could take another shot I shall. Thank you!

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d52b38109b89d346334cc0bc582328d6131fe720

commit d52b38109b89d346334cc0bc582328d6131fe720
Author: lushnikov <lushnikov@chromium.org>
Date: Wed Jan 25 09:11:59 2017

Revert of DevTools: Correct Source Panel Show/Hide Toolbar buttons (patchset #1 id:1 of https://codereview.chromium.org/2600493002/ )

Reason for revert:
It turned out the icons are actually wrong. Compare:
- Without this patch (correct): http://imgur.com/a/eFCnz
- With this patch (incorrect): http://imgur.com/a/gJ24q

Original issue's description:
> DevTools: Correct Source Panel Show/Hide Toolbar buttons
>
> Regression : Misalignment of 'Hide Navigator' and 'Hide Debugger' buttons is seen in devtools.
>
> Flipped mask positions and removed—now unnecessary—rotation transforms around show/hide panel icon containers.
>
> BUG= 671930 
> R=lushnikov@chromium.org
> TEST=Open Dev Tools, open Sources Pane, observe show/hide sidebar buttons
> are correctly aligned.  crbug.com/671930 
>
> Review-Url: https://codereview.chromium.org/2600493002
> Cr-Commit-Position: refs/heads/master@{#445339}
> Committed: https://chromium.googlesource.com/chromium/src/+/4d2364eb32a5b242790324536efccd843cb81aa8

TBR=dgozman@chromium.org,pfeldman@chromium.org,me@jakehendy.com
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG= 671930 

Review-Url: https://codereview.chromium.org/2655793003
Cr-Commit-Position: refs/heads/master@{#445983}

[modify] https://crrev.com/d52b38109b89d346334cc0bc582328d6131fe720/AUTHORS
[modify] https://crrev.com/d52b38109b89d346334cc0bc582328d6131fe720/third_party/WebKit/Source/devtools/front_end/ui/Icon.js

@lushnikov apologies for delay. I somehow managed to hose my dev environment and ended up reinstalling Windows.

I've submitted https://codereview.chromium.org/2658363003/ which has an image (http://imgur.com/a/FHN3q) proving the correctness of the icons as well.

Thanks!

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/711b0a82a640608bf4e069b9398ec415e2b8b20a

commit 711b0a82a640608bf4e069b9398ec415e2b8b20a
Author: me <me@jakehendy.com>
Date: Mon Jan 30 14:21:43 2017

Dev Tools: Adjust Dev Tool Source panel show/hide sidebar icons

Instead of rotating icons for the right hand side, flip the icons along the x-axis.

BUG= 671930 
R=lushnikov@chromium.org

Review-Url: https://codereview.chromium.org/2658363003
Cr-Commit-Position: refs/heads/master@{#446978}

[modify] https://crrev.com/711b0a82a640608bf4e069b9398ec415e2b8b20a/AUTHORS
[modify] https://crrev.com/711b0a82a640608bf4e069b9398ec415e2b8b20a/third_party/WebKit/Source/devtools/front_end/ui/Icon.js