Change Identity Service to expose CoreAccountInfo

We are currently splitting AccountInfo into Core and Extended variants.
The core variant has all the info available synchronously, while the
extended variant has additional info fetched asynchronously.

Wherever possible, we are reworking clients to use the Core variant for
clarity. All of the consumers of the Identity Service require only the
info present in the Core variant, and we anticipate this continuing to
be the case (the consumers that require the extended info are typically
UI). Hence, this CL changes the Identity Service Mojo APIs to talk in
terms of CoreAccountInfo.

CQ_INCLUDE_TRYBOTS=luci.chrome.try:linux-chromeos-chrome

Bug: 952832
Change-Id: I69cd46472843c99ac5182a1eedef9a6755cc5fce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1571646
Auto-Submit: Pâris Meuleman <pmeuleman@chromium.org>
Commit-Queue: Yue Li <updowndota@chromium.org>
Reviewed-by: Yue Li <updowndota@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Reviewed-by: Michael Giuffrida <michaelpg@chromium.org>
Reviewed-by: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654241}
22 files changed