I was trying to run telemetry for Android WebView so built/installed monochrome_public_apk. Everything appeared to work except telemetry wasn't using webview from MonochromePublic.apk I had installed. This was on a Pixel C version 8.1.0.

Steps to reproduce:
$ ninja -C out/droid monochrome_public_apk
$ out/droid/bin/monochrome_public_apk install -v
$ ./tools/perf/run_benchmark run -v --browser=android-webview --pageset-repeat=1 --also-run-disabled-tests --story-filter=browse.media.youtube --chromium-output-directory=/chrome/src/out/droid system_health.common_mobile

The telemetry benchmark ran and there was a log line that seemed like it was using MonochromePublic.apk.

"Installing /chrome/src/out/droid/apks/MonochromePublic.apk on device if needed."

However the benchmark wasn't using MonochromePublic.apk. I was able add CHECK(false) in key areas and it didn't crash. Telemetry used some other version of webview without my changes. Trying to switch the webview implementation via adb fails:

$ adb shell cmd webviewupdate set-webview-implementation org.chromium.chrome
Failed to switch to org.chromium.chrome, the WebView implementation is now provided by com.android.chrome.

It was probably user error and I'm not sure what I was doing wrong with monochrome_public_apk. perezju@ pointed me at instructions for replacing SystemWebView.apk and that worked as expected. perezju@ also asked that I file a bug about telemetry warning if not able to switch webview providers.