chromium/chrome/android/webapk/libs/runtime_library/src/README

The runtime library contains:
1) Implementation of the WebAPK service. The service implements functionality
which Chrome delegates to the WebAPK such as displaying notifications.
2) Logic to send intent to Chrome to launch Chrome in WebAPK mode.

The library is loaded by a ShellAPK which contains the WebAPK's manifest and
code to load the runtime library.

The latest version of the runtime library is extracted from Chrome's APK by the
ShellAPK when it is launched. Since the ShellAPK is updated asynchronously, the
runtime library may run within an old ShellAPK. For instance, the ShellAPK's
Android manifest may be missing some of the permissions that the runtime library
is expecting.

The number in runtime_library_version.gni must be incremented whenever the
runtime library is updated. The WebAPK re-extracts the runtime library from the
Chrome APK when the version number is incremented.