New protected method NetworkManagerBase::GetNetworksInternal

Bug: webrtc:13869
Change-Id: Ib41a705362cd45ce894db6a119226844b719b706
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/257302
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36420}

rtc_base/network.h

@@ -250,6 +250,10 @@ class RTC_EXPORT NetworkManagerBase : public NetworkManager {
 
   Network* GetNetworkFromAddress(const rtc::IPAddress& ip) const;
 
+  // To enable subclasses to get the networks list, without interfering with
+  // refactoring of the interface GetNetworks method.
+  const NetworkList& GetNetworksInternal() const { return networks_; }
+
  private:
   friend class NetworkTest;