Revert of Delete "shutdown without closing browsers" path

ash/shell_delegate.h

Index: ash/shell_delegate.h
diff --git a/ash/shell_delegate.h b/ash/shell_delegate.h
index 9a4ac77cc343b869b4c40835ba26196c059972f4..ba28e0ca26cf941c3737507dac9193f368272067 100644
--- a/ash/shell_delegate.h
+++ b/ash/shell_delegate.h
@@ -76,9 +76,8 @@
   // can perform tasks necessary before the shell is initialized.
   virtual void PreInit() = 0;
 
-  // Called at the beginninig of Shell destructor so that
-  // delegate can use Shell instance to perform cleanup tasks.
-  virtual void PreShutdown() = 0;
+  // Shuts down the environment.
+  virtual void Shutdown() = 0;
 
   // Invoked when the user uses Ctrl-Shift-Q to close chrome.
   virtual void Exit() = 0;