[NetworkChangeNotifier] Run Windows connection type computation on other thread

net/base/network_change_notifier_win.h

Index: net/base/network_change_notifier_win.h
diff --git a/net/base/network_change_notifier_win.h b/net/base/network_change_notifier_win.h
index 94bab7f8d100213744e72863ebb4a2b0aa6b51b8..687149945d162637e77e5f53c48c119e024d2e18 100644
--- a/net/base/network_change_notifier_win.h
+++ b/net/base/network_change_notifier_win.h
@@ -9,6 +9,7 @@
 
 #include <memory>
 
+#include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
@@ -62,15 +63,21 @@ class NET_EXPORT_PRIVATE NetworkChangeNotifierWin
   // 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_|.