GitLab

Screenshots: https://drive.google.com/open?id=0B1B1Up4p2NRMc28yXzJuRFRZbWs&authuser=1

TL; DR:
- never show a drop down arrow in the button. This means we can do s/MenuButton/LabelButton
- if there is one local, non-signed in profile, show a tiny button with a generic avatar
- in all other cases, show the avatar button with the profile name
- updated the button insets so that the icons are centered correctly in the button
- the new tab button should completely slide under the avatar button
- because of this, I made public the new tab button width (and height, to be consistent)

BUG=410946

Review URL: https://codereview.chromium.org/598163002

Cr-Commit-Position: refs/heads/master@{#296959}