cros: Don't send duplicate UserSession mojo messages to ash

After the profile is loaded the SessionControllerClient in the browser
sends an updated ash::mojom::UserSession to ash. Most of the time the
message is the same as the one just sent when the session was started.

BUG=714689,712799
TEST=added to SessionControllerClientTest in unit_tests

Review-Url: https://codereview.chromium.org/2842693002
Cr-Commit-Position: refs/heads/master@{#467172}
3 files changed