Using the per-revision bisect providing the bisect results,
Good build: 56.0.2903.0 (Revision: 428431).
Bad build: 56.0.2906.0 (Revision: 428890).

You are probably looking for a change made after 428515 (known good), but no later than 428516 (first known bad).
CHANGELOG URL:
  https://chromium.googlesource.com/chromium/src/+log/d509d739efec6c000cea40aae5e24f8b432cf3d5..beee5025a4557f5ea443e7583aa508a26d85ad3d

@einbinder -- 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.

M56 Beta promotion is scheduled on Dec 6 & RC cut on Monday, Dec 5 @ 4.00 PM PST.

einbinder@ please take a look ASAP

Please have a fix  before M56 hits stable.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/60923e44a7116db275bf8c74b1cd52ba2335b1af

commit 60923e44a7116db275bf8c74b1cd52ba2335b1af
Author: einbinder <einbinder@chromium.org>
Date: Wed Dec 07 00:27:42 2016

DevTools: Fix SuggestBox not showing without a maximum height

BUG= 670581 

Review-Url: https://codereview.chromium.org/2554173002
Cr-Commit-Position: refs/heads/master@{#436775}

[modify] https://crrev.com/60923e44a7116db275bf8c74b1cd52ba2335b1af/third_party/WebKit/Source/devtools/front_end/ui/SuggestBox.js

Thanks for the fix, we will verify in latest canary. If all looks good please request a merge to M56.

With response to comment #7:

Above issue is fixed on Latest Mac canary 57.0.2946.0 (Official Build) 38c3eb61c737a8d3313ca8cd31b0c514c9d35b05-refs/heads/master@{#437422}

Just to update,
Above issue is also fixed on Windows(7,8,8.1,10) and Linux(14.04 LTS) OS in latest canary 57.0.2946.0 build.

If there is no pending work, please request a merge to M56.

Issue is still seen on latest beta 56.0.2924.28	.

einbinder@, Could you please merge the fix to M56 if there is no pending work.

Please request a merge to M56 since its fixed in canary.

FYI: Your bug is labelled as Stable Release Block, please make sure to land the fix and get it merged into the release branch ASAP so we can take it for next week's Beta release for Desktop. Thank you!

Issue is still seen on latest beta 56.0.2924.51.

einbinder@ - Could you please merge the fix to M56 as this issue has been marked as release block stable.

Thanks...!!

Just to update, issue is still seen on mac 10.12.2 using latest beta #56.0.2924.59.

einbinder@ - Friendly ping...!!

Could you please merge the fix to M56 as this issue has been marked as release block stable.

Thanks...!!

einbinder@, Gentle Ping!

Could you please merge the fix to M56

This bug requires manual review: Request affecting a post-stable build
Please contact the milestone owner if you have questions.
Owners: amineer@(clank), cmasso@(bling), gkihumba@(cros), bustamante@(desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Approving on behalf of Richard.

Already merged.

https://chromium.googlesource.com/chromium/src.git/+/f854fb0bd110ef02f0a8408aae412917ab54adcd

Tested the issue on windows 7, Linux Ubuntu 14.04 and Mac 10.12.2 using chrome version 56.0.2924.87.

1. Unwanted faint underline is seen below ‘Regex’ and ‘Hide data URLs’ check boxes.
2. Suggestions list is not displayed after entering alphabets like ‘d’, ‘m’.

But 3.still Unable to delete text from ‘Filter’ text box using Backspace key.

Please find the attached screen shot for the same.
einbinder@ Please confirm on this behavior.

Thanks,

Deleted: 670581.png 86.1 KB

	670581.png 86.1 KB View Download

The fix did not work for M56, please resolve for M57.

A friendly reminder that M57 Stable is launch is coming VERY soon! Your bug is labelled as Stable ReleaseBlock, pls make sure to land the fix and get it merged into the release branch (2987) ASAP so it gets enough baking time in Beta (before Stable promotion). Thank you!

URGENT - PTAL ASAP.

We're getting VERY close to M57 Stable promotion. And 
this issue is marked as M57 stable release blocker. Pls make sure to land the fix and get it merged into the release branch ASAP so it gets enough baking time in Beta (before Stable promotion).

Know that this issue shouldn't block the release?  Remove the ReleaseBlock-Stable label or move to M58.

Thank you.

I am seeing this fixed in 57.