aura: Implement new app list mock.

ash/shell_delegate.h

Index: ash/shell_delegate.h
diff --git a/ash/shell_delegate.h b/ash/shell_delegate.h
index 55b1a687a9cc4fcf8872b94be668b98fc4e48547..d54152482d15556c92489e9406c51a3ab685b1be 100644
--- a/ash/shell_delegate.h
+++ b/ash/shell_delegate.h
@@ -22,7 +22,6 @@ class Widget;
 
 namespace ash {
 
-class AppListModel;
 class AppListViewDelegate;
 class LauncherDelegate;
 class LauncherModel;
@@ -61,9 +60,6 @@ class ASH_EXPORT ShellDelegate {
   // Invoked when a user uses Ctrl-Shift-Q to close chrome.
   virtual void Exit() = 0;
 
-  // Invoked to ask the delegate to populate the |model|.
-  virtual void BuildAppListModel(AppListModel* model) = 0;
-
   // Invoked to create an AppListViewDelegate. Shell takes the ownership of
   // the created delegate.
   virtual AppListViewDelegate* CreateAppListViewDelegate() = 0;