First failure:
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/KitKat%20Phone%20Tester%20%28dbg%29/11004

Commit range:
http://test-results.appspot.com/revision_range?start=618125&end=618130 (6 commits)

Where the following sounds very much related:
r618129 Set BrowserClient in SetupOnMainThread for DoNotTrackTest

Not reverting since that appears to be a fix for another failure, but please have a look and investigate ASAP.

Logs for the failed test look like:

C 1239.855s Main  [ RUN      ] DoNotTrackTest.NotEnabled
C 1239.855s Main  [WARNING:dns_config_service_posix.cc(334)] Failed to read DnsConfig.
C 1239.855s Main  [WARNING:child_process_launcher_helper_posix.cc(124)] Ignoring invalid file assets/snapshot_blob_64.bin
C 1239.855s Main  [WARNING:simple_synchronous_entry.cc(1251)] Could not open platform files for entry.
C 1239.855s Main  [WARNING:browser_test_utils.cc(638)] Last navigation to http://127.0.0.1:41453/echoheader?DNT failed with net error 0
C 1239.855s Main  [WARNING:browser_test_utils.cc(586)] No last committed entry
C 1239.855s Main  ../../content/browser/do_not_track_browsertest.cc:122: Failure
C 1239.855s Main  Value of: NavigateToURL(shell(), GetURL("/echoheader?DNT"))
C 1239.855s Main    Actual: false
C 1239.855s Main  Expected: true
C 1239.855s Main  Stack trace:
C 1239.855s Main  
C 1239.855s Main  Reading Android symbols from: /b/swarming/w/ir
C 1239.855s Main  Searching for Chrome symbols from within: /b/swarming/w/ir/out/Debug/lib.unstripped:/b/swarming/w/ir/out/Debug
C 1239.855s Main  Searching for native crashes in: /b/swarming/w/itj8tQcZ/tmpRnVnjm
C 1239.855s Main  Unknown Android release, consider passing --packed-lib.
C 1239.855s Main  Searching for Chrome symbols from within: /b/swarming/w/ir/out/Debug/lib.unstripped:/b/swarming/w/ir/out/Debug
C 1239.855s Main  
C 1239.855s Main  Stack Trace:
C 1239.856s Main    RELADDR   FUNCTION                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   FILE:LINE
C 1239.856s Main    01914087  testing::internal::AssertHelper::operator=(testing::Message const&) const                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  ../../third_party/googletest/src/googletest/src/gtest.cc:421:25
C 1239.856s Main    0116bc6b  content::(anonymous namespace)::DoNotTrackTest_NotEnabled_Test::RunTestOnMainThread()                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      ../../content/browser/do_not_track_browsertest.cc:122:3
C 1239.856s Main    02f6ba29  content::BrowserTestBase::ProxyRunTestOnMainThreadLoop()                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   ../../content/public/test/browser_test_base.cc:447:5
C 1239.856s Main    0118d7a5  void base::internal::Invoker<base::internal::BindState<void (content::GenerateMHTMLAndExitRendererMessageFilter::*)(), base::internal::UnretainedWrapper<content::GenerateMHTMLAndExitRendererMessageFilter> >, void ()>::RunImpl<void (content::GenerateMHTMLAndExitRendererMessageFilter::*)(), std::__1::tuple<base::internal::UnretainedWrapper<content::GenerateMHTMLAndExitRendererMessageFilter> >, 0u>(void (content::GenerateMHTMLAndExitRendererMessageFilter::*&&)(), std::__1::tuple<base::internal::UnretainedWrapper<content::GenerateMHTMLAndExitRendererMessageFilter> >&&, std::__1::integer_sequence<unsigned int, 0u>)  ../../base/bind_internal.h:689:12
C 1239.856s Main    02fcbba9  content::ShellBrowserMainParts::PreMainMessageLoopRun()                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    ../../content/shell/browser/shell_browser_main_parts.cc:177:26
C 1239.856s Main    01b7cb59  content::BrowserMainLoop::PreMainMessageLoopRun()                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          ../../content/browser/browser_main_loop.cc:983:13
C 1239.856s Main    01b7db21  int base::internal::Invoker<base::internal::BindState<int (content::BrowserMainLoop::*)(), base::internal::UnretainedWrapper<content::BrowserMainLoop> >, int ()>::RunImpl<int (content::BrowserMainLoop::* const&)(), std::__1::tuple<base::internal::UnretainedWrapper<content::BrowserMainLoop> > const&, 0u>(int (content::BrowserMainLoop::* const&)(), std::__1::tuple<base::internal::UnretainedWrapper<content::BrowserMainLoop> > const&, std::__1::integer_sequence<unsigned int, 0u>)                                                                                                                                           ../../base/bind_internal.h:689:12
C 1239.856s Main    01da77a5  content::StartupTaskRunner::RunAllTasksNow()                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               ../../content/browser/startup_task_runner.cc:41:18
C 1239.856s Main    01b7c327  content::BrowserMainLoop::CreateStartupTasks()                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             ../../content/browser/browser_main_loop.cc:912:27
C 1239.856s Main    01b7ddf9  content::BrowserMainRunnerImpl::Initialize(content::MainFunctionParams const&)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             ../../content/browser/browser_main_runner_impl.cc:144:15
C 1239.856s Main    01b7b285  content::BrowserMain(content::MainFunctionParams const&)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   ../../content/browser/browser_main.cc:43:32
C 1239.856s Main    02f6b845  content::BrowserTestBase::SetUp()                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          ../../content/public/test/browser_test_base.cc:344:3
C 1239.856s Main    02f5de71  content::ContentBrowserTest::SetUp()                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       ../../content/public/test/content_browser_test.cc:102:20
C 1239.856s Main    01917463  testing::Test::Run()                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       ../../third_party/googletest/src/googletest/src/gtest.cc:2517:3

Disabling test at:
https://chromium-review.googlesource.com/c/chromium/src/+/1388465

Issue 917126 has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b82592bb8608129a25781fe9a663304d69fc38e9

commit b82592bb8608129a25781fe9a663304d69fc38e9
Author: Juan Antonio Navarro Perez <perezju@chromium.org>
Date: Fri Dec 21 11:53:09 2018

Disable failing DoNotTrackTest.NotEnabled on Android

TBR=kinuko@chromium.org,shimazu@chromium.org

Bug:  916978 
Change-Id: Iacab5593389fdf6128974e91caef093da8ed97ae
Reviewed-on: https://chromium-review.googlesource.com/c/1388465
Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Commit-Queue: Juan Antonio Navarro Pérez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618503}
[modify] https://crrev.com/b82592bb8608129a25781fe9a663304d69fc38e9/content/browser/do_not_track_browsertest.cc

Test disabled. Reducing Pri and removing from sheriff's queue.

Thanks. Created a CL for the fix: crrev.com/c/1390032.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2112209118b6f3129406dd7e4531ae45028629ce

commit 2112209118b6f3129406dd7e4531ae45028629ce
Author: Makoto Shimazu <shimazu@chromium.org>
Date: Wed Dec 26 03:25:26 2018

Enable DoNotTrackTest.NotEnabled

crrev.com/c/1382669 started to set BrowserClient on an older Android, and it caused
test failures. This CL is to skip setting custom BrowserClient for a KitKat or older Android.

Bug:  916978 
Change-Id: Ia6a7a9be71ffdba9539a72eceff3883c710527af
Reviewed-on: https://chromium-review.googlesource.com/c/1390032
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618902}
[modify] https://crrev.com/2112209118b6f3129406dd7e4531ae45028629ce/content/browser/do_not_track_browsertest.cc