assistant: avoid notifying duplicate state changes

Also moved some mojom service registration to later stage during
initialization.  This prevented crash during autotest because the tests
are much faster than human when enabling the service which caused the UI
to call into Assistant service before the libassistant components are
ready.

Bug: b:79879622
Test: run a localy autotest that invokes this new api
Change-Id: I643d0388115fa2690fa059b73b83748f8d06c335
Reviewed-on: https://chromium-review.googlesource.com/c/1330751
Reviewed-by: Tao Wu <wutao@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607293}
2 files changed