Ideally we would like to get to the situation where we could "freeze" the browser_options after having parsed them from the command line.

However, browser_options.extensions_to_load is currently a list of mutable ExtensionToLoad objects. It seems that these objects _have to_ be mutable since their extension_id may depend on the path to the extension after it has been (possibly) copied to a remote device [2].

I suggest making browser_options.extensions_to_load a plain list of strings with the paths to the extensions to load. Then possible_browser.SetUpEnvironment can create and manage the lifetime of the necessary ExtensionToLoad objects.

+achuith since looking at the clients of extensions_to_load it seems that this is mainly used for CrOS to load 'auto_test' and an 'easy_unlock' app.

[1]: https://cs.chromium.org/chromium/src/third_party/catapult/telemetry/telemetry/internal/browser/extension_to_load.py?rcl=12ffa89339910751ca0516770d7b8877f4dd25a3&l=15
[2]: https://cs.chromium.org/chromium/src/third_party/catapult/telemetry/telemetry/internal/browser/extension_to_load.py?rcl=12ffa89339910751ca0516770d7b8877f4dd25a3&l=39
[3]: https://cs.chromium.org/search/?q=extensions_to_load+file:%5C.py$+-file:%5Esrc/third_party/android_tools+-file:%5Einfra/infra/services/android_docker&type=cs