[NetworkChangeNotifier] Run Windows connection type computation on other thread

net/base/network_change_notifier_win.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_BASE_NETWORK_CHANGE_NOTIFIER_WIN_H_
 #define NET_BASE_NETWORK_CHANGE_NOTIFIER_WIN_H_
 
 #include <windows.h>
 
 #include <memory>
 
+#include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/timer/timer.h"
 #include "base/win/object_watcher.h"
 #include "net/base/net_export.h"
 #include "net/base/network_change_notifier.h"
 
 namespace net {
@@ skipping 33 matching lines @@
   ConnectionType GetCurrentConnectionType() const override;
 
   // ObjectWatcher::Delegate methods:
   // Must only be called on the thread |this| was created on.
   void OnObjectSignaled(HANDLE object) override;
 
   // Does the actual work to determine the current connection type.
   // It is not thread safe, see crbug.com/324913.
   virtual ConnectionType RecomputeCurrentConnectionType() const;
 
+  // Calls RecomputeCurrentConnectionTypeImpl on the DNS thread and runs
+  // |reply_callback| with the type on the calling thread.
+  virtual void RecomputeCurrentConnectionTypeOnDnsThread(
+      base::Callback<void(ConnectionType)> reply_callback) const;

[pauljensen, 2017/05/26 18:29:40]

Instead of having every caller assemble the Callback by Binding the method to a
weakptr, you could make this function take a C++ pointer-to-member-function and
just have one Bind call inside this function.  It might simplify the code
slightly.  This is one of the very rare instances where C++
pointer-to-member-function is useful...it'd be a pity to pass it up :)  But it's
up to you.

[jkarlin, 2017/05/26 19:03:58]

Passing callbacks is more general however. I'd rather stick with that.

+
   void SetCurrentConnectionType(ConnectionType connection_type);
 
   // Notifies IP address change observers of a change immediately, and notifies
   // network state change observers on a delay.  Must only be called on the
   // thread |this| was created on.
-  void NotifyObservers();
+  void NotifyObservers(ConnectionType connection_type);
 
   // Forwards connection type notifications to parent class.
   void NotifyParentOfConnectionTypeChange();
+  void NotifyParentOfConnectionTypeChangeImpl(ConnectionType connection_type);
 
   // Tries to start listening for a single subsequent address change.  Returns
   // false on failure.  The caller is responsible for updating |is_watching_|.
   // Virtual for unit tests.  Must only be called on the thread |this| was
   // created on.
   virtual bool WatchForAddressChangeInternal();
 
   static NetworkChangeCalculatorParams NetworkChangeCalculatorParamsWin();
 
   // All member variables may only be accessed on the thread |this| was created
@@ skipping 26 matching lines @@
 
   // Used for calling WatchForAddressChange again on failure.
   base::WeakPtrFactory<NetworkChangeNotifierWin> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkChangeNotifierWin);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_NETWORK_CHANGE_NOTIFIER_WIN_H_