Add Editor::onDidAdd/RemoveSelection

Also update EditorComponent to use the new ::onDidAddSelection method.

src/editor-component.coffee

@@ -33,7 +33,6 @@ EditorComponent = React.createClass
   updateRequestedWhilePaused: false
   cursorMoved: false
   selectionChanged: false
-  selectionAdded: false
   scrollingVertically: false
   mouseWheelScreenRow: null
   mouseWheelScreenRowClearDelay: 150
@@ -347,8 +346,7 @@ EditorComponent = React.createClass
     {editor} = @props
     @subscribe editor, 'screen-lines-changed', @onScreenLinesChanged
     @subscribe editor.onDidAddCursor(@onCursorAdded)
-    @subscribe editor, 'selection-removed selection-screen-range-changed', @onSelectionChanged
-    @subscribe editor, 'selection-added', @onSelectionAdded
+    @subscribe editor.onDidAddSelection(@onSelectionAdded)
     @subscribe editor, 'decoration-added', @onDecorationChanged
     @subscribe editor, 'decoration-removed', @onDecorationChanged
     @subscribe editor, 'decoration-changed', @onDecorationChanged
@@ -721,17 +719,22 @@ EditorComponent = React.createClass
     @pendingChanges.push(change)
     @requestUpdate() if editor.intersectsVisibleRowRange(change.start, change.end + 1) # TODO: Use closed-open intervals for change events
 
-  onSelectionChanged: (selection) ->
+  onSelectionAdded: (selection) ->
     {editor} = @props
+
+    @subscribe selection, 'screen-range-changed', => @onSelectionChanged(selection)
+    @subscribe selection, 'destroyed', =>
+      @onSelectionChanged(selection)
+      @unsubscribe(selection)
+
     if editor.selectionIntersectsVisibleRowRange(selection)
       @selectionChanged = true
       @requestUpdate()
 
-  onSelectionAdded: (selection) ->
+  onSelectionChanged: (selection) ->
     {editor} = @props
     if editor.selectionIntersectsVisibleRowRange(selection)
       @selectionChanged = true
-      @selectionAdded = true
       @requestUpdate()
 
   onScrollTopChanged: ->

src/editor.coffee

@@ -324,6 +324,12 @@ class Editor extends Model
   onDidRemoveCursor: (callback) ->
     @emitter.on 'did-remove-cursor', callback
 
+  onDidAddSelection: (callback) ->
+    @emitter.on 'did-add-selection', callback
+
+  onDidRemoveSelection: (callback) ->
+    @emitter.on 'did-remove-selection', callback
+
   # Retrieves the current {TextBuffer}.
   getBuffer: -> @buffer
 
@@ -2315,12 +2321,14 @@ class Editor extends Model
           return selection
     else
       @emit 'selection-added', selection
+      @emitter.emit 'did-add-selection', selection
       selection
 
   # Remove the given selection.
   removeSelection: (selection) ->
     _.remove(@selections, selection)
     @emit 'selection-removed', selection
+    @emitter.emit 'did-remove-selection', selection
 
   # Reduce one or more selections to a single empty selection based on the most
   # recently added cursor.