Correct class/structure declaration order.

1. Correct the class/struct declaration order to be IAW
   the Google C++ style guide[1].
2. For non-copyable classes, switched from non-implemented
   private methods to explicitly deleted[2] methods.
3. Minor const and member initialization fixes.

[1] https://google.github.io/styleguide/cppguide.html#Declaration_Order
[2] http://eel.is/c++draft/dcl.fct.def.delete

PiperOrigin-RevId: 246521844

util/env_windows.cc

@@ -626,21 +626,19 @@ class WindowsEnv : public Env {
   }
 
  private:
+  // Entry per Schedule() call
+  struct BGItem {
+    void* arg;
+    void (*function)(void*);
+  };
+
   // BGThread() is the body of the background thread
   void BGThread();
 
   std::mutex mu_;
   std::condition_variable bgsignal_;
   bool started_bgthread_;
-
-  // Entry per Schedule() call
-  struct BGItem {
-    void* arg;
-    void (*function)(void*);
-  };
-  typedef std::deque<BGItem> BGQueue;
-  BGQueue queue_;
-
+  std::deque<BGItem> queue_;
   Limiter mmap_limiter_;
 };