Follow-up to https://bugs.chromium.org/p/chromium/issues/detail?id=891377:

Port protocol::Binary to 
components/autofill_assistant/browser/devtools/devtools_api/client_api_generator.py and friends.

This means that we'll need to add the protocol::Binary type to the protocol string utility for autofill_assistant, and probably tweak the templates a bit, similar to the changes needed for headless.

Until then, autofill_assistant will be using protocol::String.

We should also explore reducing the code duplication, e.g. avoiding to have forks of the client api generator and templates.