Commandline flags

Applying flags

Note: this requires either a userdebug or eng Android build (you can check with adb shell getprop Flags cannot be enabled on production builds of Android.

WebView reads flags from a specific file during startup. To enable flags, write to the file with:

# Overwrite flags (supports multiple)
build/android/adb_system_webview_command_line \
    --show-composited-layer-borders \
# Clear flags
build/android/adb_system_webview_command_line ""
# Print flags

Or, for a locally compiled APK:

autoninja -C out/Default system_webview_apk
# Overwrite flags (supports multiple)
out/Default/bin/system_webview_apk argv --args='--show-composited-layer-borders --log-net-log=foo.json'
# Clear flags
out/Default/bin/system_webview_apk argv --args=''
# Print flags
out/Default/bin/system_webview_apk argv

Or, you can use the adb in your $PATH like so:

# Overwrite flags
adb shell "echo '_ --show-composited-layer-borders' > ${FLAG_FILE}"
# The first token is ignored. We use '_' as a convenient placeholder, but any
# token is acceptable.

Applying Features with flags

WebView supports the same --enable-features=feature1,feature2 and --disable-features=feature3,feature4 syntax as the rest of Chromium. You can use these like any other flag. Please consult base/feature_list.h for details.

Interesting flags

WebView supports any flags supported in any layer we depend on (ex. content). Some interesting flags and Features:

  • --show-composited-layer-borders
  • --enable-features=NetworkService,NetworkServiceInProcess
  • --log-net-log=<filename.json>

WebView also defines its own flags and Features: