Always update display layer before emitting a marker layer update event

Previously, when a change was happening outside of a transaction (e.g.
undo, redo, etc.), we were emitting a marker layer update event as soon
as we spliced each marker layer. This was causing display layers to be
out of date when the marker layer event occurred and could therefore
cause problems if users performed a display layer query display layer
inside the update event.

With this commit, marker layer update events will now always be emitted
after updating display layers, thus fixing the errors we were observing
in Atom (https://circleci.com/gh/atom/atom/2806).

spec/marker-layer-spec.coffee

@@ -179,6 +179,9 @@ describe "MarkerLayer", ->
     it "notifies observers at the end of the outermost transaction when markers are created, updated, or destroyed", ->
       [marker1, marker2] = []
 
+      displayLayer = buffer.addDisplayLayer()
+      displayLayerDidChange = false
+
       updateCount = 0
       layer1.onDidUpdate ->
         updateCount++
@@ -193,6 +196,8 @@ describe "MarkerLayer", ->
         else if updateCount is 3
           marker1.destroy()
           marker2.destroy()
+        else if updateCount is 6
+          expect(displayLayerDidChange).toBe(true, 'Display layer was updated after marker layer.')
 
       buffer.transact ->
         buffer.transact ->
@@ -205,6 +210,12 @@ describe "MarkerLayer", ->
       layer1.markRange([[0, 2], [0, 4]])
       expect(updateCount).toBe(5)
 
+      # update events happen after updating display layers when there is no parent transaction.
+      displayLayer.onDidChangeSync ->
+        displayLayerDidChange = true
+      buffer.undo()
+      expect(updateCount).toBe(6)
+
   describe "::clear()", ->
     it "destroys all of the layer's markers", (done) ->
       buffer = new TextBuffer(text: 'abc')

src/marker-layer.coffee

@@ -272,7 +272,6 @@ class MarkerLayer
           marker.destroy()
         else
           marker.valid = false
-    @delegate.markersUpdated(this)
 
   restoreFromSnapshot: (snapshots) ->
     return unless snapshots?

src/text-buffer.coffee

@@ -737,19 +737,25 @@ class TextBuffer
     newRange
 
   emitDidChangeEvent: (changeEvent) ->
-    # 1. Emit the change event on all the registered text decoration layers.
+    # Emit the change event on all the registered text decoration layers.
     @textDecorationLayers.forEach (textDecorationLayer) ->
       textDecorationLayer.bufferDidChange(changeEvent)
-    # 2. Emit the change event on all the registered display layers.
+    # Emit the change event on all the registered display layers.
     changeEventsByDisplayLayer = new Map()
     for id, displayLayer of @displayLayers
       event = displayLayer.bufferDidChange(changeEvent)
       changeEventsByDisplayLayer.set(displayLayer, event)
-    # 3. Emit a normal `did-change` event for other subscribers too.
+    # Emit a normal `did-change` event for other subscribers too.
     @emitter.emit 'did-change', changeEvent
-    # 4. Emit a `did-change-sync` event from all the registered display layers.
+    # Emit a `did-change-sync` event from all the registered display layers.
     changeEventsByDisplayLayer.forEach (event, displayLayer) ->
       displayLayer.emitDidChangeSyncEvent(event)
+    # Emit a `did-update` event from all the registered marker layers. If this
+    # happens inside a nested transaction, the event will be emitted at the end
+    # of the outermost transaction.
+    if @markerLayers?
+      for id, markerLayer of @markerLayers
+        @markersUpdated(markerLayer)
 
   # Public: Delete the text in the given range.
   #