Currently these browser_tests are failing:
PDFTestFiles/PDFExtensionTest.Load/8
PDFTestFiles/PDFExtensionTest.Load/4
PDFExtensionTest.PdfAccessibilityCharCountCrash

This started with this roll on Nov 2:
https://chromium-review.googlesource.com/c/chromium/src/+/751103

These are the relevant changes:
https://pdfium.googlesource.com/pdfium.git/+log/87d06d37e0d0..565fb438dd4a

$ git log 87d06d37e..565fb438d --date=short --no-merges --format='%ad %ae %s'
2017-11-02 art-snake Unify CPDF_DataAvail::Check[Header/End].
2017-11-02 art-snake Improve readability for CPDF_Parser::StartParseInternal
2017-11-02 art-snake Unify parsing of linearized header.
2017-11-02 asweintraub Only use the yield instruction on architectures that support it.

I suspect the ones by Artem.

We maintain two bots that run tests in official builds:
https://build.chromium.org/p/chromium.clang/builders/ToTWin%20tester
https://build.chromium.org/p/chromium.clang/builders/CrWinClangLLD%20tester

First failing build:
https://build.chromium.org/p/chromium.clang/builders/ToTWin%20tester/builds/81

Logs:
https://logs.chromium.org/v/?s=chromium%2Fbb%2Fchromium.clang%2FToTWin_tester%2F81%2F%2B%2Frecipes%2Fsteps%2Fbrowser_tests%2F0%2Flogs%2FPDFTestFiles__x2f_PDFExtensionTest.Load__x2f_8%2F0

[ RUN      ] PDFTestFiles/PDFExtensionTest.Load/8
[7964:6892:1102/174717.473:WARNING:chrome_browser_main_win.cc(613)] Command line too long for RegisterApplicationRestart:  --brave-new-test-launcher --cfi-diag=0 --gtest_also_run_disabled_tests --gtest_filter=PDFTestFiles/PDFExtensionTest.Load/8 --single_process --test-launcher-bot-mode --test-launcher-output="C:\Users\CHROME~2\AppData\Local\Temp\scoped_dir5108_9101\results5108_18628\test_results.xml" --test-launcher-summary-output="e:\b\s\w\iozh4cjv\output.json" --user-data-dir="C:\Users\CHROME~2\AppData\Local\Temp\scoped_dir5108_9101\d5108_1188" --disable-offline-auto-reload --site-per-process --no-first-run --no-default-browser-check --enable-logging=stderr --safebrowsing-disable-auto-update --disable-default-apps --wm-window-animations-disabled --disable-component-update --test-type=browser --force-color-profile=srgb --disable-zero-browsers-open-for-tests --ipc-connection-timeout=30 --allow-file-access-from-files --dom-automation --log-gpu-control-list-decisions --disable-backgrounding-occluded-windows --disable-gl-drawing-for-tests --override-use-software-gl-for-tests --force-color-profile=srgb --disable-features=NetworkPrediction --flag-switches-begin --flag-switches-end --restore-last-session about:blank
[7964:6892:1102/174717.631:INFO:pdf_extension_test.cc(231)] Loading: pdf_private/3d_pdf_unsupported.pdf
[7964:3872:1102/174717.695:WARNING:embedded_test_server.cc(228)] Request not handled. Returning 404: /favicon.ico
[7964:6940:1102/174717.852:ERROR:service_manager.cc(158)] Connection InterfaceProviderSpec prevented service: content_renderer from binding interface: blink::mojom::ReportingServiceProxy exposed by: content_browser
[7964:6892:1102/174717.853:INFO:CONSOLE(0)] "Styling master document from stylesheets defined in HTML Imports is deprecated, and is planned to be removed in M65, around March 2018. Please refer to https://goo.gl/EGXzpw for possible migration paths.", source:  (0)
[7964:6892:1102/174718.513:INFO:pdf_extension_test.cc(231)] Loading: pdf_private/81807.pdf
[7964:6940:1102/174718.748:ERROR:service_manager.cc(158)] Connection InterfaceProviderSpec prevented service: content_renderer from binding interface: blink::mojom::ReportingServiceProxy exposed by: content_browser
[7964:6892:1102/174718.748:INFO:CONSOLE(0)] "Styling master document from stylesheets defined in HTML Imports is deprecated, and is planned to be removed in M65, around March 2018. Please refer to https://goo.gl/EGXzpw for possible migration paths.", source:  (0)
[7964:6892:1102/174719.249:INFO:pdf_extension_test.cc(231)] Loading: pdf_private/accessibility_crash_1.pdf
[7964:6940:1102/174719.500:ERROR:service_manager.cc(158)] Connection InterfaceProviderSpec prevented service: content_renderer from binding interface: blink::mojom::ReportingServiceProxy exposed by: content_browser
[7964:6892:1102/174719.505:INFO:CONSOLE(0)] "Styling master document from stylesheets defined in HTML Imports is deprecated, and is planned to be removed in M65, around March 2018. Please refer to https://goo.gl/EGXzpw for possible migration paths.", source:  (0)
../../chrome/browser/pdf/pdf_extension_test.cc(233): error:       Expected: !PdfIsExpectedToFailLoad(pdf_file)
      Which is: true
To be equal to: success
      Which is: false