Using the per-revision bisect providing the bisect results,
Good build:56.0.2897.0(Revision:426673).
Bad build: 56.0.2899.0(Revision:426989).

You are probably looking for a change made after 426912 (known good), but no later than 426913 (first known bad).

CHANGELOG URL:

The script might not always return single CL as suspect as some perf builds might get missing due to failure.

  https://chromium.googlesource.com/chromium/src/+log/58290e535d3de7a235e13b6f023b1c8bf06a223a..7c3d7bbd510eda2bcfb971f6d166da26bcfe4222

From the CL above, assigning the issue to the concern owner 

@lfg- Could you please check whether this is caused with respect to your change, if not please help us in assigning it to the right owner.

Review-Url: https://chromiumcodereview.appspot.com/2415973002

Thanks !

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4b746a0ef62cc611f7b79b4cc6a2d7cebb982f3e

commit 4b746a0ef62cc611f7b79b4cc6a2d7cebb982f3e
Author: lfg <lfg@chromium.org>
Date: Mon Oct 24 17:24:58 2016

Revert of Do not hide the old RenderWidgetHostView when commiting a navigation. (patchset #2 id:20001 of https://codereview.chromium.org/2415973002/ )

Reason for revert:
Caused a regression on Mac.

BUG= 658688 

Original issue's description:
> Do not hide the old RenderWidgetHostView when commiting a navigation.
>
> This fixes an issue where the old RenderView is reused by a new remote
> subframe. We shouldn't be leaking resources, because now we are already
> hiding the unused RenderView in the renderer, when the local main frame
> gets detached and the WebViewFrameWidget is closed.
>
> BUG= 638375 
> CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation
>
> Committed: https://crrev.com/7c3d7bbd510eda2bcfb971f6d166da26bcfe4222
> Cr-Commit-Position: refs/heads/master@{#426913}

TBR=creis@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG= 638375 

Review-Url: https://codereview.chromium.org/2448503002
Cr-Commit-Position: refs/heads/master@{#427091}

[modify] https://crrev.com/4b746a0ef62cc611f7b79b4cc6a2d7cebb982f3e/content/browser/frame_host/render_frame_host_manager.cc
[modify] https://crrev.com/4b746a0ef62cc611f7b79b4cc6a2d7cebb982f3e/content/browser/site_per_process_browsertest.cc

Rechecked this on chrome version 56.0.2900.0 on MAC 10.11.6, fix is working as intended. No blank page is displayed when clicked on "Help" / "?" icon for the options available in "chrome://md-settings/siteSettings" Page.

Adding TE-Verified labels.

Just to update, rechecked this on chrome version 56.0.2902.0 on MAC 10.11.6, fix is working as intended. No blank page is displayed when clicked on "Help" / "?" icon for the options available in "chrome://md-settings/siteSettings" Page.

 Issue 658643  has been merged into this issue.