Store mode object in Buffer

src/atom/buffer.coffee

@@ -91,9 +91,10 @@ class Buffer
     if not @path then throw new Error("Tried to save buffer with no url")
     fs.write @path, @getText()
 
-  modeName: ->
+  getMode: ->
+    return @mode if @mode
     extension = if @path then @path.split('/').pop().split('.').pop() else null
-    switch extension
+    modeName = switch extension
       when 'js' then 'javascript'
       when 'coffee' then 'coffee'
       when 'rb', 'ru' then 'ruby'
@@ -102,4 +103,7 @@ class Buffer
       when 'css' then 'css'
       else 'text'
 
+    @mode = new (require("ace/mode/#{modeName}").Mode)
+
+
 _.extend(Buffer.prototype, EventEmitter)

src/atom/highlighter.coffee

@@ -5,18 +5,12 @@ EventEmitter = require 'event-emitter'
 module.exports =
 class Highlighter
   buffer: null
-  tokenizer: null
   screenLines: []
 
   constructor: (@buffer) ->
-    @buildTokenizer()
     @screenLines = @buildLinesForScreenRows('start', 0, @buffer.lastRow())
     @buffer.on 'change', (e) => @handleBufferChange(e)
 
-  buildTokenizer: ->
-    Mode = require("ace/mode/#{@buffer.modeName()}").Mode
-    @tokenizer = (new Mode).getTokenizer()
-
   handleBufferChange: (e) ->
     oldRange = e.oldRange.copy()
     newRange = e.newRange.copy()
@@ -56,8 +50,9 @@ class Highlighter
       screenLine
 
   buildLineForScreenRow: (state, row) ->
+    tokenizer = @buffer.getMode().getTokenizer()
     line = @buffer.getLine(row)
-    {tokens, state} = @tokenizer.getLineTokens(line, state)
+    {tokens, state} = tokenizer.getLineTokens(line, state)
     new ScreenLineFragment(tokens, line, [1, 0], [1, 0], { state })
 
   lineForScreenRow: (row) ->