Most of these are relatively straightforward:

PrivateAPIDrive fetches access tokens for the primary account via google_apis::AuthService
PrivateAPIMisc does the same thing
EnterprisePlatformKeysPrivateAPI: Include looks stale
ChromeFeedbackPrivateDelegate has a public wrapper that returns the email address of the signed-in user
WebstorePrivateAPI returns the signed-in user’s email to the JS side
ExternalComponentLoader’s include looks stale
ExtensionDownloader gets access tokens for the active account via IdentityProvider. This one is not turnkey: Need to check whether this is for PO2TS, DeviceO2TS, or both.

In addition, there is relevant code for app_shell:
//extensions IdentityAPI fetches access tokens via ShellOAuth2TokenService.
//extensions ShellOAuth2TokenService implements OAuth2TokenService.

We'll need to figure out the app_shell question: Is this code relevant going forward? If so, does it need to be converted to use the Identity Service?