Recent build of Chromium (and probably Chrome Canary build as well) has got another interesting feature along with the Omnibox history sync. This optional feature enables users to automatically sign-in to Google Sites (like Gmail, YouTube etc.) if they have opted for Chrome’s built-in synchronization feature.
Although, this is not “truly” automatic and users are required to confirm the infobar prompt. In order to enjoy this feature, users should have opted for synchronizing their browsing data and personal preferences using their Google Account. The following video explains this: