Deprecated: The Log Verbosifier app does not work on Android R. M84 is the last milestone to support this for other OS levels.
Instead, use the webview-verbose-logging flag in WebView DevTools (added in M83). This flag behaves exactly the same as if the Log Verbosifier app is installed, but will be compatible with all OS levels (including Android R). The log format is identical, so you can search logcat as before.
WebView Log Verbosifier is an empty app (in fact, it cannot be launched). However, if this app is installed, WebView will log the active field trials and CommandLine flags, for debugging/QA purposes. An empty app is used because it can be installed on any device (including user builds, where field trials are still relevant).
We no longer support building the log verbosifier from source. Googlers can get a prebuilt copy of the log verbosifier. External contributors can request a precompiled copy by emailing the WebView team.
You can grep the logcat like so:
adb logcat | grep -i 'Active field trial' # Field trials, one per line adb logcat | grep -i 'WebViewCommandLine' # CommandLine switches, one per line adb logcat | grep -iE 'Active field trial|WebViewCommandLine' # Both
Then just start up any WebView app.
When you're done investigating flags/field trials, you can disable the logging by uninstalling the app:
adb uninstall org.chromium.webview_log_verbosifier