Emit 'marker-added/removed' events when buffer marker validity changes

spec/app/text-buffer-spec.coffee

@@ -1185,6 +1185,17 @@ describe 'Buffer', ->
           expect(marker4.isValid()).toBeTruthy()
           expect(marker4.getRange()).toEqual [[4, 20], [4, 23]]
 
+      it "emits 'marker-added' and 'marker-removed' events when markers are invalidated or revalidated", ->
+        marker2.destroy()
+        marker3.destroy()
+        markerRemovedHandler.reset()
+
+        buffer.change([[4, 21], [4, 24]], "foo")
+        expect(markerRemovedHandler).toHaveBeenCalledWith(marker1)
+
+        buffer.undo()
+        expect(markerAddedHandler).toHaveBeenCalledWith(marker1)
+
     describe ".markersForPosition(position)", ->
       it "returns all markers that intersect the given position", ->
         m1 = buffer.markRange([[3, 4], [3, 10]])

src/app/buffer-marker.coffee

@@ -260,10 +260,12 @@ class BufferMarker
     delete @buffer.validMarkers[@id]
     @buffer.invalidMarkers[@id] = this
     @notifyObservers(bufferChanged: true)
+    @buffer.trigger 'marker-removed', this
 
   revalidate: ->
     delete @buffer.invalidMarkers[@id]
     @buffer.validMarkers[@id] = this
     @notifyObservers(bufferChanged: true)
+    @buffer.trigger 'marker-added', this
 
 _.extend BufferMarker.prototype, EventEmitter