Findit identified the culprit r561165 with confidence 70.0% in the config "chromium.win / Win7 Tests (dbg)(1)"
based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVyywELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKUAWNocm9taXVtLndpbi9XaW43IFRlc3RzIChkYmcpKDEpLzY5MzM5L3Zpel9jb250ZW50X2Jyb3dzZXJ0ZXN0cy9WMlZpVW5SalIyVjBWWE5sY2sxbFpHbGhRbkp2ZDNObGNsUmxjM1F1VkdWemRFZGxkRlZ6WlhKTlpXUnBZVUZ6Y0dWamRGSmhkR2x2TVZSdk1TOHgMCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA


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Feedback is welcome! Please use component Tools>Test>FindIt>Flakiness

This appears to flake on Win10. The culprit identified in #1 has nothing to do with the test and is likely incorrect.

Flakiness dashboard: https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=content_browsertests&tests=WebRtcGetUserMediaBrowserTest.TestGetUserMediaAspectRatio1To1%2F1

Here's what a failure of the test looks like:
[ RUN      ] WebRtcGetUserMediaBrowserTest.TestGetUserMediaAspectRatio1To1/1
DevTools listening on ws://127.0.0.1:65498/devtools/browser/c01c9d30-93b5-43fd-b1d1-c12ebb4c55cf
[2244:1608:0529/112220.666:INFO:CONSOLE(202)] "Calling getUserMediaAndAnalyseAndStop.", source: http://127.0.0.1:65499/media/getusermedia.html (202)
../../content/browser/webrtc/webrtc_getusermedia_browsertest.cc(565): error: Expected equality of these values:
  "w=320:h=320"
  ExecuteJavascriptAndReturnResult(constraints_1_1)
    Which is: "Error: VideoElement width and height set to 0.\n    at failTest (http://127.0.0.1:65499/media/webrtc_test_utilities.js:30:17)\n    at detectorFunction (http://127.0.0.1:65499/media/getusermedia.html:402:9)"
With diff:
@@ -1,1 +1,3 @@
-w=320:h=320
+Error: VideoElement width and height set to 0.
+    at failTest (http://127.0.0.1:65499/media/webrtc_test_utilities.js:30:17)
+    at detectorFunction (http://127.0.0.1:65499/media/getusermedia.html:402:9)
Stack trace:
Backtrace:
	testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop [0x00007FF65E70826B+87]
	testing::internal::AssertHelper::operator= [0x00007FF65E707E10+78]
	content::WebRtcGetUserMediaBrowserTest_TestGetUserMediaAspectRatio1To1_Test::RunTestOnMainThread [0x00007FF65E11447C+604]
	content::BrowserTestBase::ProxyRunTestOnMainThreadLoop [0x00007FF65F771635+477]
	content::ShellBrowserMainParts::PreMainMessageLoopRun [0x00007FF65FF57452+68]
	content::BrowserMainLoop::PreMainMessageLoopRun [0x00007FF65E9DBCB5+85]
	content::StartupTaskRunner::RunAllTasksNow [0x00007FF65ECE2CC4+28]
	content::BrowserMainLoop::CreateStartupTasks [0x00007FF65E9DA7B2+736]
	content::BrowserMainRunnerImpl::Initialize [0x00007FF65E9DE07F+129]
	content::BrowserMainRunnerImpl::Initialize [0x00007FF65E9DDFE7+37]
	ShellBrowserMain [0x00007FF661DD6318+24]
	content::ShellMainDelegate::RunProcess [0x00007FF661DD4BFC+218]
	content::RunBrowserProcessMain [0x00007FF65E91BD9F+99]
	content::ContentMainRunnerImpl::Run [0x00007FF65E91C76E+364]
	service_manager::Main [0x00007FF65FBE36A7+1711]
	content::ContentMain [0x00007FF65E91BCE1+65]
	content::BrowserTestBase::SetUp [0x00007FF65F771323+1757]
	content::ContentBrowserTest::SetUp [0x00007FF65F768A6C+136]

Flakiness seems to be better now.