With Chrome 37 now released, there is a new API available, identity.getProfileUserInfo. I am not really sure what information this is meant to return or what it represents.
From the documentation, I thought it would return the email address and id of the user signed into Chrome(i.e. from the hamburger menu), however this is not really true- when I call it(from the context of an extension, which requests the "identity" permission), I get the id of the user signed in that way(and if I paste that after plus.google.com/ I get their G+ page), but the email field is blank. Is that intended?