The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e542c9d7d6337ee9236a8c7cc29a76f1a1a0f007

commit e542c9d7d6337ee9236a8c7cc29a76f1a1a0f007
Author: Kinuko Yasuda <kinuko@chromium.org>
Date: Wed Aug 01 08:16:34 2018

Disable PreviewsNoScriptBrowserTest.NoScriptPreviewsEnabled on Linux

Because they seem to be flaky on Linux Xenial.

TBR=tbansal

Bug: 869781
Change-Id: I8a396d51256b67e6ef3d5d6e9d4ae4cda365ad1b
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/1158120
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579725}
[modify] https://crrev.com/e542c9d7d6337ee9236a8c7cc29a76f1a1a0f007/chrome/browser/previews/previews_browsertest.cc

FWIW, I ran the test multiple times locally by:
 ninja -C out/out-gn3 browser_tests -j1000 -l25 && out/out-gn3/browser_tests --gtest_filter=*PreviewsNoScript* --gtest_also_run_disabled_tests --gtest_repeat=100 --gtest_break_on_failure

I think it flaked on 6th run.

Tarun, thanks for the command! 
Unfoturnately I'm not having luck repro-ing so far (2 x 100 runs). I wonder if actually depends on Xenial version of Linux.

I am trying it again. Let me see if I can get it to flake again.

I got it to flake again. Stack:

[158142:158142:0911/085303.902392:WARNING:gaia_auth_fetcher.cc(991)] Could not reach Google Accounts servers: errno -11
[158142:158303:0911/085304.002146:WARNING:embedded_test_server.cc(238)] Request not handled. Returning 404: /noscript_test.js
[158142:158303:0911/085304.124901:WARNING:embedded_test_server.cc(238)] Request not handled. Returning 404: /favicon.ico
../../chrome/browser/previews/previews_browsertest.cc:245: Failure
Value of: noscript_css_requested()
  Actual: false
Expected: true
Stack trace:
#0 0x0000049e7150 StackTraceGetter::CurrentStackTrace()
#1 0x000004a086f7 testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop()
#2 0x000004a07b5d testing::internal::AssertHelper::operator=()
#3 0x000003031333 PreviewsNoScriptBrowserTest_DISABLED_NoScriptPreviewsEnabledHttpRedirectToHttps_Test::RunTestOnMainThread()
#4 0x000007cce853 content::BrowserTestBase::ProxyRunTestOnMainThreadLoop()
#5 0x0000025513fd _ZN4base8internal13FunctorTraitsIM25RenderViewContextMenuBaseFvvEvE6InvokeIS4_P21RenderViewContextMenuJEEEvT_OT0_DpOT1_

For some reason, the flake reproduces on my local desktop, but not on Doug's. As discussed on Wednesday, I am taking over the bug since it's easier for me to repro it.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/14b1518c493d16df552e8755ad2ccb67ad42fb33

commit 14b1518c493d16df552e8755ad2ccb67ad42fb33
Author: Tarun Bansal <tbansal@chromium.org>
Date: Fri Sep 14 20:56:58 2018

Reenable some of the NoScript browser tests

Reenable some of the flaky NoScript browser tests.
This CL includes two fixes:
1. Ensure that some of thread unsafe variables are not
referenced cross-thread.
2. Disables loading of blacklist database which is racy with the
first page load. At least one of the test flakes that I
reproduced locally was because of this.

Change-Id: If3c7190532f5feebf686f02dd9a3003e7396f9f4
Bug: 869781
Reviewed-on: https://chromium-review.googlesource.com/1226851
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#591470}
[modify] https://crrev.com/14b1518c493d16df552e8755ad2ccb67ad42fb33/chrome/browser/previews/previews_browsertest.cc

AFAIK, only flaky test left is PreviewsOptimizationGuideBrowserTest::NoScriptPreviewsEnabledByWhitelist.

Refreshed during triage

Refreshed during triage