Preserve focus when switching between pane items

If the pane is currently focused, when showing a view associated with
a new item, focus that view.

spec/app/pane-spec.coffee

@@ -44,6 +44,15 @@ describe "Pane", ->
       expect(itemChangedHandler.argsForCall[0][1]).toBe editSession1
       itemChangedHandler.reset()
 
+    describe "if the pane's active view is focused before calling showItem", ->
+      it "focuses the new active view", ->
+        container.attachToDom()
+        pane.focus()
+        expect(pane.activeView).not.toBe view2
+        expect(pane.activeView).toMatchSelector ':focus'
+        pane.showItem(view2)
+        expect(view2).toMatchSelector ':focus'
+
     describe "when the given item isn't yet in the items list on the pane", ->
       view3 = null
       beforeEach ->

src/app/pane.coffee

@@ -73,11 +73,13 @@ class Pane extends View
 
   showItem: (item) ->
     return if item is @activeItem
+    isFocused = @is(':has(:focus)')
     @addItem(item)
     view = @viewForItem(item)
     @itemViews.children().not(view).hide()
     @itemViews.append(view) unless view.parent().is(@itemViews)
     view.show()
+    view.focus() if isFocused
     @activeItem = item
     @activeView = view
     @trigger 'pane:active-item-changed', [item]