Use atom.workspace.getView to construct WorkspaceViews

It returns the root DOM node of the workspace. Eventually this will
be a custom element but for now it’s just a DOM node with a
__spacePenView reference on it.

src/atom.coffee

@@ -582,7 +582,7 @@ class Atom extends Model
 
     startTime = Date.now()
     @workspace = Workspace.deserialize(@state.workspace) ? new Workspace
-    @workspaceView = new WorkspaceView(@workspace)
+    @workspaceView = @workspace.getView(@workspace).__spacePenView
     @deserializeTimings.workspace = Date.now() - startTime
 
     @keymaps.defaultTarget = @workspaceView[0]

src/workspace.coffee

@@ -10,6 +10,7 @@ Editor = require './editor'
 PaneContainer = require './pane-container'
 Pane = require './pane'
 {jQuery} = require './space-pen-extensions'
+WorkspaceView = null
 
 # Essential: Represents the state of the user interface for the entire window.
 # An instance of this class is available via the `atom.workspace` global.
@@ -66,6 +67,9 @@ class Workspace extends Model
     fullScreen: atom.isFullScreen()
     packagesWithActiveGrammars: @getPackageNamesWithActiveGrammars()
 
+  getViewClass: ->
+    WorkspaceView ?= require './workspace-view'
+
   getPackageNamesWithActiveGrammars: ->
     packageNames = []
     addGrammar = ({includedGrammarScopes, packageName}={}) ->