AtlasKit Dropdown was recently updated to support fitting the
width of its container. However, AtlasKit Button, the trigger
element currently used for the dropdowns, does not fit the width
of AtlasKit Dropdown and stll has text overflowing out of its
button when there is an iconBefore prop passed in. Instead of
using AtlasKit Button, use a div and mimic the button look. This
allows the "button" to fit the container width and can display
ellipsized text within itself.