Move checkoutHead implementation to Editor

src/editor.coffee

@@ -586,8 +586,10 @@ class Editor extends View
     @showIndentGuide = showIndentGuide
     @resetDisplay()
 
-  # {Delegates to: TextBuffer.checkoutHead}
-  checkoutHead: -> @getBuffer().checkoutHead()
+  # Checkout the HEAD revision of this editor's file.
+  checkoutHead: ->
+    if path = @getPath()
+      @project.getRepo()?.checkoutHead(path)
 
   # {Delegates to: EditSession.setText}
   setText: (text) -> @activeEditSession.setText(text)

src/text-buffer.coffee

@@ -632,12 +632,6 @@ class TextBuffer extends Model
         return match[0][0] != '\t'
     undefined
 
-  # Checks out the current `HEAD` revision of the file.
-  checkoutHead: ->
-    path = @getPath()
-    return unless path
-    @project.getRepo()?.checkoutHead(path)
-
   ### Internal ###
 
   transact: (fn) -> @text.transact fn