This looks flaky; there are some green builds in between builds that are seeing this test fail.

First failing build: https://ci.chromium.org/buildbot/chromium.clang/ToTWin/1681

Logs: https://logs.chromium.org/v/?s=chromium%2Fbb%2Fchromium.clang%2FToTWin%2F1681%2F%2B%2Frecipes%2Fsteps%2Fnetwork_service_browser_tests%2F0%2Fstdout

Excerpt:
[ RUN      ] PDFTestFiles/PDFExtensionLoadTest.Load/4
[5088:5656:0614/180951.507:WARNING:chrome_browser_main_win.cc(655)] Command line too long for RegisterApplicationRestart:  --brave-new-test-launcher --cfi-diag=0 --gtest_also_run_disabled_tests --gtest_filter=PDFTestFiles/PDFExtensionLoadTest.Load/4 --single_process --test-launcher-bot-mode --test-launcher-filter-file=../../testing/buildbot/filters/mojo.fyi.network_browser_tests.filter --test-launcher-output="C:\Users\CHROME~2\AppData\Local\Temp\scoped_dir5628_19612\results5628_27398\test_results.xml" --test-launcher-summary-output="e:\b\s\w\ioquz84t\output.json" --user-data-dir="C:\Users\CHROME~2\AppData\Local\Temp\scoped_dir5628_19612\d5628_14150" --disable-offline-auto-reload --site-per-process --no-first-run --no-default-browser-check --enable-logging=stderr --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-compositor-ukm-for-tests --enable-features=NetworkService,TestFeatureForBrowserTest1 --disable-features=NetworkPrediction,SpeculativePreconnect,TestFeatureForBrowserTest2 --flag-switches-begin --flag-switches-end --restore-last-session about:blank
[5088:7388:0614/180951.526:WARNING:discovery_network_list_win.cc(195)] Failed to open Wlan client handle: 1062
[5088:5656:0614/180951.634:INFO:pdf_extension_test.cc(250)] Loading: pdf_private/cfuzz5.pdf
[5088:7868:0614/180951.689:WARNING:embedded_test_server.cc(229)] Request not handled. Returning 404: /favicon.ico
[5088:5656:0614/180951.839:INFO:CONSOLE(0)] "Styling master document from stylesheets defined in HTML Imports is deprecated. Please refer to https://goo.gl/EGXzpw for possible migration paths.", source:  (0)
../../chrome/browser/pdf/pdf_extension_test.cc(252): error: Expected equality of these values:
  PdfIsExpectedToLoad(pdf_file)
    Which is: false
  success
    Which is: true
pdf_private/cfuzz5.pdf
Google Test trace:
../../chrome/browser/pdf/pdf_extension_test.cc(248): pdf_private/cfuzz5.pdf
Stack trace:
Backtrace:
	StackTraceGetter::CurrentStackTrace [0x01FB09D4+40]
	testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop [0x01FB90EB+69]
	testing::internal::AssertHelper::operator= [0x01FB8D50+48]
	PDFExtensionTest::LoadAllPdfsTest [0x01665E22+1032]
	PDFExtensionLoadTest_Load_Test::RunTestOnMainThread [0x016659CA+88]
	content::BrowserTestBase::ProxyRunTestOnMainThreadLoop [0x035F7987+357]
	ChromeBrowserMainParts::PreMainMessageLoopRunImpl [0x04368394+3346]
	ChromeBrowserMainParts::PreMainMessageLoopRun [0x043675C5+145]
	content::BrowserMainLoop::PreMainMessageLoopRun [0x027818DA+68]
	content::StartupTaskRunner::RunAllTasksNow [0x02A160A3+23]
	content::BrowserMainLoop::CreateStartupTasks [0x0278083D+615]
	content::BrowserMainRunnerImpl::Initialize [0x027837BF+107]
	content::BrowserMain [0x0277EF18+160]
	content::RunBrowserProcessMain [0x035058DD+117]
	content::ContentMainRunnerImpl::Run [0x0350603B+333]
	service_manager::Main [0x03A57988+1168]
	content::ContentMain [0x0350580F+51]
	content::BrowserTestBase::SetUp [0x035F7760+1498]
[5088:5656:0614/180952.566:INFO:pdf_extension_test.cc(250)] Loading: pdf_private/fw4.pdf
[5088:5656:0614/180952.806:INFO:CONSOLE(0)] "Styling master document from stylesheets defined in HTML Imports is deprecated. Please refer to https://goo.gl/EGXzpw for possible migration paths.", source:  (0)
[5088:8700:0614/180953.344:ERROR:browser_process_sub_thread.cc(216)] Waited 11 ms for network service
[5088:5656:0614/180953.347:WARNING:pref_notifier_impl.cc(23)] Pref observer found at shutdown.
[5088:5656:0614/180953.347:WARNING:pref_notifier_impl.cc(23)] Pref observer found at shutdown.
[  FAILED  ] PDFTestFiles/PDFExtensionLoadTest.Load/4, where GetParam() = 4 (1926 ms)
[679/860] PDFTestFiles/PDFExtensionLoadTest.Load/4 (2053 ms)