Add library for working with the menubar
Merge pull request #1 from ahal/menubar_lib

Add library for working with the menubar
Add functionality for switching and retrieving tabs to the tabs library
Merge pull request #2 from ahal/tabs_lib

Add functionality for switching and retrieving tabs to the tabs library
Fix some tests that break with e10s enabled
Use 'chrome' context by default
Add ability to close a tab
Merge pull request #4 from ahal/tabs_lib

Add ability to close a tab