WIP: Render gutters before initial measurement

The shouldUpdate method is just returning true for now. We probably need
to find a new approach to representing line number decorations that's
easier to diff, perhaps a sparse array?

src/text-editor.coffee

@@ -2671,7 +2671,6 @@ class TextEditor extends Model
     _.last(@selections)
 
   getSelectionAtScreenPosition: (position) ->
-    debugger if global.debug
     markers = @selectionsMarkerLayer.findMarkers(containsScreenPosition: position)
     if markers.length > 0
       @cursorsByMarkerId.get(markers[0].id).selection
@@ -3405,6 +3404,9 @@ class TextEditor extends Model
   getGutters: ->
     @gutterContainer.getGutters()
 
+  getLineNumberGutter: ->
+    @lineNumberGutter
+
   # Essential: Get the gutter with the given name.
   #
   # Returns a {Gutter}, or `null` if no gutter exists for the given name.