Schedule redraw when updating an invisible editor

The redrawOnReattach flag will now be set when update
display is called on an invisible editor so that if the
editor is detached or hidden before the next update was
processed it will be performed when reattached.

spec/app/editor-spec.coffee

@@ -2515,3 +2515,21 @@ describe "Editor", ->
 
         runs ->
           expect(editor.renderedLines.find('.line').text()).toBe 'hidden changes'
+
+      it "redraws the editor when it is next reattached", ->
+        editor.attachToDom()
+        editor.hide()
+        editor.setText('hidden changes')
+        editor.setCursorBufferPosition([0,4])
+        editor.detach()
+
+        displayUpdatedHandler = jasmine.createSpy("displayUpdatedHandler")
+        editor.on 'editor:display-updated', displayUpdatedHandler
+        editor.show()
+        editor.attachToDom()
+
+        waitsFor ->
+          displayUpdatedHandler.callCount is 1
+
+        runs ->
+          expect(editor.renderedLines.find('.line').text()).toBe 'hidden changes'

src/app/editor.coffee

@@ -783,7 +783,9 @@ class Editor extends View
   updateDisplay: (options={}) ->
     return unless @attached and @activeEditSession
     return if @activeEditSession.destroyed
-    return unless @isVisible()
+    unless @isVisible()
+      @redrawOnReattach = true
+      return
 
     @updateRenderedLines()
     @highlightCursorLine()