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:

$ # Overwrites all flags (and prints the new flag state):
$ build/android/adb_system_webview_command_line \
    --show-composited-layer-borders \
    --log-net-log=foo.json # Supports multiple flags
$ # Simply prints the existing flag state:
$ build/android/adb_system_webview_command_line
$ # Passing empty string clears all flags:
$ build/android/adb_system_webview_command_line ""

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

$ FLAG_FILE=/data/local/tmp/webview-command-line
$ 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.
Note: either set of commands will overwrite existing flags.

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: