Serialize EditSession's buffer's id instead of its path

src/app/edit-session.coffee

@@ -21,7 +21,7 @@ class EditSession
 
   ### Internal ###
 
-  @version: 2
+  @version: 3
 
   @deserialize: (state) ->
     new EditSession(state)
@@ -38,7 +38,7 @@ class EditSession
       project.editSessions.push(this)
       @state = optionsOrState
       {tabLength, softTabs, @softWrap} = @state.toObject()
-      @buffer = project.bufferForPath(@state.get('bufferPath'))
+      @buffer = project.bufferForId(@state.get('bufferId'))
       @setScrollTop(@state.get('scrollTop'))
       @setScrollLeft(@state.get('scrollLeft'))
       cursorScreenPosition = @state.getObject('cursorScreenPosition')
@@ -98,7 +98,7 @@ class EditSession
 
   serialize: ->
     @state.set
-      bufferPath: @buffer.getPath()
+      bufferId: @buffer.id
       scrollTop: @getScrollTop()
       scrollLeft: @getScrollLeft()
       tabLength: @getTabLength()

src/app/project.coffee

@@ -232,6 +232,9 @@ class Project
     else
       @buildBuffer(null, text)
 
+  bufferForId: (id) ->
+    _.find @buffers, (buffer) -> buffer.id is id
+
   # Given a file path, this sets its {Buffer}.
   #
   # filePath - A {String} representing a path

src/app/text-buffer.coffee

@@ -7,6 +7,7 @@ EventEmitter = require 'event-emitter'
 UndoManager = require 'undo-manager'
 BufferChangeOperation = require 'buffer-change-operation'
 BufferMarker = require 'buffer-marker'
+guid = require 'guid'
 
 # Public: Represents the contents of a file.
 #
@@ -15,8 +16,7 @@ BufferMarker = require 'buffer-marker'
 module.exports =
 class TextBuffer
   @acceptsDocuments: true
-  @version: 1
-  @idCounter: 1
+  @version: 2
   registerDeserializer(this)
 
   @deserialize: (state) ->
@@ -38,7 +38,6 @@ class TextBuffer
   # path - A {String} representing the file path
   # initialText - A {String} setting the starting text
   constructor: (args...) ->
-    @id = @constructor.idCounter++
     @nextMarkerId = 1
     @validMarkers = {}
     @invalidMarkers = {}
@@ -47,10 +46,15 @@ class TextBuffer
       @state = args[0]
       @text = @state.get('text')
       path = @state.get('path')
+      @id = @state.get('id')
     else
       [path, initialText] = args
       @text = telepath.Document.create(initialText, shareStrings: true) if initialText
-      @state = telepath.Document.create(deserializer: @constructor.name, version: @constructor.version)
+      @id = guid.create().toString()
+      @state = telepath.Document.create
+        id: @id
+        deserializer: @constructor.name
+        version: @constructor.version
 
     if path
       @setPath(path)