Tab bar contains:

• Tabs for the subapps of the currently open app.
• Subapps tabs have an active state and an inactive state.
• First tab is always the browser subapp. It cannot be closed – doesn't have a Close button.
• Other tabs are typically closable (default behavior) but can also be configured as closable=false. 
• Tab bar has close button to close the app itself.
•  View buttons (tree, list, thumbnail) are part of the contained app, not part of the Tab bar.

UI specification https://app.zeplin.io/project/5acc848ede054e0a4865f805/dashboard