Emit 'marker-added/removed' events on DisplayBuffer

spec/app/display-buffer-spec.coffee

@@ -737,3 +737,22 @@ describe "DisplayBuffer", ->
         marker.destroy()
         expect(marker.isValid()).toBeFalsy()
         expect(displayBuffer.getMarker(marker.id)).toBeUndefined()
+
+    describe "marker-added and marker-removed events", ->
+      it "emits the appropriate event when a marker is created, destroyed, or its validity changes", ->
+        displayBuffer.on 'marker-added', markerAddedHandler = jasmine.createSpy("markerAddedHandler")
+        displayBuffer.on 'marker-removed', markerRemovedHandler = jasmine.createSpy("markerRemovedHandler")
+
+        marker = displayBuffer.markBufferRange([[5, 4], [5, 10]])
+        expect(markerAddedHandler).toHaveBeenCalledWith(marker)
+        markerAddedHandler.reset()
+
+        buffer.change([[5, 3], [5, 11]], 'hey')
+        expect(markerRemovedHandler).toHaveBeenCalledWith(marker)
+        markerRemovedHandler.reset()
+
+        buffer.undo()
+        expect(markerAddedHandler).toHaveBeenCalledWith(marker)
+
+        marker.destroy()
+        expect(markerRemovedHandler).toHaveBeenCalledWith(marker)

src/app/display-buffer.coffee

@@ -33,6 +33,12 @@ class DisplayBuffer
     @tokenizedBuffer.on 'grammar-changed', (grammar) => @trigger 'grammar-changed', grammar
     @tokenizedBuffer.on 'changed', @handleTokenizedBufferChange
     @buffer.on 'markers-updated', @handleMarkersUpdated
+    @buffer.on 'marker-added', (marker) =>
+      @trigger 'marker-added', @getMarker(marker.id)
+    @buffer.on 'marker-removed', (marker) =>
+      marker = @getMarker(marker.id)
+      delete @markers[marker.id]
+      @trigger 'marker-removed', marker
 
   buildLineMap: ->
     @lineMap = new LineMap
@@ -468,7 +474,7 @@ class DisplayBuffer
   #
   # Returns the {DisplayBufferMarker} (if it exists).
   getMarker: (id) ->
-    @markers[id] ? do =>
+    @markers[id] ?= do =>
       if bufferMarker = @buffer.getMarker(id)
         new DisplayBufferMarker({bufferMarker, displayBuffer: this})
 
@@ -548,7 +554,6 @@ class DisplayBuffer
   ###
   # Internal #
   ###
-
   pauseMarkerObservers: ->
     marker.pauseEvents() for marker in @getMarkers()