Apply 'scrollbar-style-x' class to WorkspaceView

…where x is 'overlay' or 'legacy' depending on whether the scrollbars
are only visible when scrolling (overlay) or always visible (legacy).

This will allow us to style scrollbars in legacy mode without forcing
them to be visible in overlay mode.

src/workspace-view.coffee

@@ -3,6 +3,7 @@ path = require 'path'
 Q = require 'q'
 _ = require 'underscore-plus'
 Delegator = require 'delegato'
+scrollbarStyle = require 'scrollbar-style'
 {$, $$, View} = require './space-pen-extensions'
 fs = require 'fs-plus'
 Workspace = require './workspace'
@@ -81,6 +82,11 @@ class WorkspaceView extends View
 
     @subscribe @model, 'uri-opened', => @trigger 'uri-opened'
 
+    @subscribe scrollbarStyle.onValue (style) =>
+      @removeClass('scrollbar-style-legacy')
+      @removeClass('scrollbar-style-overlay')
+      @addClass("scrollbar-style-#{style}")
+
     @updateTitle()
 
     @on 'focus', (e) => @handleFocus(e)