Findit identified the culprit r572540 with confidence 70.0% in the config "chromium.memory / Linux MSan Tests"
based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVyxAELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKNAWNocm9taXVtLm1lbW9yeS9MaW51eCBNU2FuIFRlc3RzLzEwNzA0L3Zpel9icm93c2VyX3Rlc3RzL1RXRjVZbVZUWlhSTlpYUmhaR0YwWVM5VFlXWmxRbkp2ZDNOcGJtZFRaWEoyYVdObFRXVjBZV1JoZEdGVVpYTjBMazFoYkhkaGNtVkpiV2N2TUE9PQwLEhNNYXN0ZXJGbGFrZUFuYWx5c2lzGAEM

If the culprit above is wrong, please file a bug using this link and hit submit:
https://bugs.chromium.org/p/chromium/issues/entry?status=Unconfirmed&labels=Pri-1,Test-Findit-Wrong&components=Tools%3ETest%3EFindit%3EFlakiness&summary=%5BFindit%5D%20Flake%20Analyzer%20-%20Wrong%20result%20for%20MaybeSetMetadata/SafeBrowsingServiceMetadataTest.MalwareImg/0&comment=Link%20to%20Analysis%3A%20https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVyxAELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKNAWNocm9taXVtLm1lbW9yeS9MaW51eCBNU2FuIFRlc3RzLzEwNzA0L3Zpel9icm93c2VyX3Rlc3RzL1RXRjVZbVZUWlhSTlpYUmhaR0YwWVM5VFlXWmxRbkp2ZDNOcGJtZFRaWEoyYVdObFRXVjBZV1JoZEdGVVpYTjBMazFoYkhkaGNtVkpiV2N2TUE9PQwLEhNNYXN0ZXJGbGFrZUFuYWx5c2lzGAEM

Automatically posted by the findit-for-me app (https://goo.gl/Ot9f7N).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b916fccec83f726c3cfe28a3040b9caddc3fc9f6

commit b916fccec83f726c3cfe28a3040b9caddc3fc9f6
Author: Makoto Shimazu <shimazu@chromium.org>
Date: Thu Jul 05 05:18:25 2018

Revert "Move Blink Sandbox IPC to Mojo Calls"

This reverts commit b993e42cacf1ed4454b4df62dfacf8eee2bec869.

Reason for revert: MSan bot failure and find-it suggested this might be the culprit. Please see  crbug.com/860349  for detail.

Failing test: MaybeSetMetadata/SafeBrowsingServiceMetadataTest.MalwareImg/0

Original change's description:
> Move Blink Sandbox IPC to Mojo Calls
> 
> Instead of Chromium IPC macro-defined messages or Mojo, Chrome on Linux
> uses hand-pickled IPC messages through a special purpose file descriptor
> to send messages from the renderer to the browser host in order to
> access FontConfig for font matching and font fallback. This system is
> described in docs/linux_sandbox_ipc.md.
> 
> For the "Font Matching by Full Font Name / PS Name" effort, see issue
> 828317, additional out of process font methods are needed. Instead of
> adding them to this legacy hand-written IPC, we modernize the Linux
> Sandbox IPC mechanism and upgrade it to using Mojo interface definitions
> and a service architecture, in which a font service running in an
> unsandboxed utility process answers FontConfig requests from the
> renderer.
> 
> Previous CLs [1], [2] prepared the Font Service to have testing and
> additional font fallback and render-style-for-strike methods. Now we can
> move Blink over to using this Mojo interface and remove the traditional
> sandbox IPC handlers since we do not use the file descriptor based IPC
> anymore for FontConfig acces.
> 
> For more details, please refer to the design doc in issue 839344.
> 
> [1] https://chromium-review.googlesource.com/c/chromium/src/+/1091754
> [2] https://chromium-review.googlesource.com/c/chromium/src/+/1087951
> 
> Bug:  855021 
> Change-Id: I0f30a726621026566f50402afed00c92940b702c
> Reviewed-on: https://chromium-review.googlesource.com/1109964
> Commit-Queue: Dominik Röttsches <drott@chromium.org>
> Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
> Reviewed-by: Michael Giuffrida <michaelpg@chromium.org>
> Reviewed-by: Robert Sesek <rsesek@chromium.org>
> Reviewed-by: Luke Halliwell <halliwell@chromium.org>
> Reviewed-by: Lei Zhang <thestig@chromium.org>
> Reviewed-by: Antoine Labour <piman@chromium.org>
> Reviewed-by: Emil A Eklund <eae@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#572540}

TBR=rkc@chromium.org,thestig@chromium.org,michaelpg@chromium.org,eae@chromium.org,skyostil@chromium.org,servolk@chromium.org,slan@chromium.org,drott@chromium.org,halliwell@chromium.org,rsesek@chromium.org,piman@chromium.org

Change-Id: I290a80ed3f36443d91ec7e082d42f01871ffdba9
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug:  855021 ,  860349 
Reviewed-on: https://chromium-review.googlesource.com/1126719
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572709}
[modify] https://crrev.com/b916fccec83f726c3cfe28a3040b9caddc3fc9f6/chrome/app/generated_resources.grd
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[modify] https://crrev.com/b916fccec83f726c3cfe28a3040b9caddc3fc9f6/content/browser/renderer_host/pepper/pepper_truetype_font_linux.cc
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[modify] https://crrev.com/b916fccec83f726c3cfe28a3040b9caddc3fc9f6/services/service_manager/sandbox/linux/sandbox_linux.h
[modify] https://crrev.com/b916fccec83f726c3cfe28a3040b9caddc3fc9f6/third_party/blink/public/BUILD.gn
[modify] https://crrev.com/b916fccec83f726c3cfe28a3040b9caddc3fc9f6/tools/metrics/histograms/enums.xml

Let's check the flakiness dashboard later if it's fixed.

Dashboard:
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=viz_browser_tests&tests=MaybeSetMetadata%2FSafeBrowsingServiceMetadataTest.MalwareImg

Dashboard looks good now. Mark this as fixed.

There was a (D)CHECK failure:

[1:1:0704/155925.217883:FATAL:font_cache.cc(404)] Check failed: false.
    #0 0x000002a9ab81 in __interceptor_backtrace /b/swarming/w/ir/kitchen-workdir/src/third_party/llvm/compiler-rt/lib/msan/../sanitizer_common/sanitizer_common_interceptors.inc:4024:13
    #1 0x00001357140f in base::debug::StackTrace::StackTrace(unsigned long) ./../../base/debug/stack_trace_posix.cc:808:41
    #2 0x000013291d20 in logging::LogMessage::~LogMessage() ./../../base/logging.cc:592:29
    #3 0x000023002eca in blink::FontCache::CrashWithFontInfo(blink::FontDescription const*) ./../../third_party/blink/renderer/platform/fonts/font_cache.cc:404:3
    #4 0x00002302c7d0 in blink::FontFallbackIterator::Next(WTF::Vector<int, 0ul, WTF::PartitionAllocator> const&) ./../../third_party/blink/renderer/platform/fonts/font_fallback_iterator.cc:121:7
    #5 0x00002302b93e in blink::FontFallbackIterator::Next(WTF::Vector<int, 0ul, WTF::PartitionAllocator> const&) ./../../third_party/blink/renderer/platform/fonts/font_fallback_iterator.cc:139:12
    #6 0x00002307b2e5 in blink::HarfBuzzShaper::ShapeSegment(blink::RangeData*, blink::RunSegmenter::RunSegmenterRange const&, blink::ShapeResult*) const ./../../third_party/blink/renderer/platform/fonts/shaping/harf_buzz_shaper.cc:842:30

On which bot, on Win7 Tests (dbg)(1)? I disabled the test on MSAN, see  issue 860445 . I believe there is a race condition in safe_browsing::ThreatDetails::OnReceivedThreatDOMDetails when run inside that harness. If there are flakes outside of MSAN, I should disable it more broadly. 

This DCHECK looks like issue 561873, which is interesting.