I can't reproduce on Linux on Chrome 52.0.2716.0; could you give more specific repro details?

If you look at the code where it crashes, you can see how you check request for being null after using it.

The specific details to repro are: open any site, security panel and reload the page...

123456

This bug has been marked as M51 Beta blocker. And we're cutting M51 Beta candidate tomorrow. Please try to resolve this ASAP.Thank you.

I cannot reproduce with a fresh build of the latest M51 tag according to https://omahaproxy.appspot.com/ . pfeldman@, are there any additional repro conditions?

Deleted: beta-51.0.2704.29.mov 14.3 MB

beta-51.0.2704.29.mov 14.3 MB Download

Turns out to be caused by service workers. pfeldman@ helped me author a fix at https://codereview.chromium.org/1938183003

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c9bfaecea4885f2dd2ba60796e998f1fb5e5d3e7

commit c9bfaecea4885f2dd2ba60796e998f1fb5e5d3e7
Author: lgarron <lgarron@chromium.org>
Date: Tue May 03 01:26:12 2016

Security panel: add listeners only to the added target.

This prevents the Security panel from getting MainFrameNavigated events from service workers.

BUG= 608113 
TEST=1. Open the native new tab page.
2. Open the DevTools Security panel.
3. Refresh
4. Wait a few seconds
The sidebar of the Security panel should show at least three sections (Main Origin, Non-Secure Origins, Secure Origins), and those sections should *not disappear*.

Review-Url: https://codereview.chromium.org/1938183003
Cr-Commit-Position: refs/heads/master@{#391142}

[modify] https://crrev.com/c9bfaecea4885f2dd2ba60796e998f1fb5e5d3e7/third_party/WebKit/Source/devtools/front_end/security/SecurityPanel.js

Fixed in M-52, will ask for merge to M-51 once it's baked on Canary.

Fix is not critical, will be merged later this week.  It is ok to push Beta tomorrow without this fix.