Factor out NetworkID and caching mechanism from n_q_e.{h,cc}

net/nqe/network_id.h

Index: net/nqe/network_id.h
diff --git a/net/nqe/network_id.h b/net/nqe/network_id.h
new file mode 100644
index 0000000000000000000000000000000000000000..f48da619567c37b7b0f62a8e96c0a5559727bcdf
--- /dev/null
+++ b/net/nqe/network_id.h
@@ -0,0 +1,63 @@
+// Copyright 2016 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_NQE_NETWORK_ID_H_
+#define NET_NQE_NETWORK_ID_H_
+
+#include <string>
+#include <tuple>
+
+#include "net/base/net_export.h"
+#include "net/base/network_change_notifier.h"
+
+namespace net {
+
+namespace nqe {
+
+namespace internal {
+
+// NetworkID is used to uniquely identify a network.
+// For the purpose of network quality estimation and caching, a network is
+// uniquely identified by a combination of |type| and
+// |id|. This approach is unable to distinguish networks with
+// same name (e.g., different Wi-Fi networks with same SSID).
+// This is a protected member to expose it to tests.
+struct NET_EXPORT_PRIVATE NetworkID {
+  NetworkID(NetworkChangeNotifier::ConnectionType type, const std::string& id)
+      : type(type), id(id) {}
+  NetworkID(const NetworkID& other) : type(other.type), id(other.id) {}
+  ~NetworkID() {}
+
+  NetworkID& operator=(const NetworkID& other) {
+    type = other.type;
+    id = other.id;
+    return *this;
+  }
+
+  // Overloaded because NetworkID is used as key in a map.

[bengr, 2016/07/19 01:04:35]

I'd remove the comment because NetworkID should not need to know how it will be
used. You could say something like "Overloaded to support ordered collections." 

[tbansal1, 2016/07/20 00:08:47]

Done.

+  bool operator<(const NetworkID& other) const {
+    return std::tie(type, id) < std::tie(other.type, other.id);
+  }
+
+  // Connection type of the network.
+  NetworkChangeNotifier::ConnectionType type;
+
+  // Name of this network. This is set to:
+  // - Wi-Fi SSID if the device is connected to a Wi-Fi access point and the
+  //   SSID name is available, or
+  // - MCC/MNC code of the cellular carrier if the device is connected to a
+  //   cellular network, or
+  // - "Ethernet" in case the device is connected to ethernet.
+  // - An empty string in all other cases or if the network name is not
+  //   exposed by platform APIs.
+  std::string id;
+};
+
+}  // namespace internal
+
+}  // namespace nqe
+
+}  // namespace net
+
+#endif  // NET_NQE_NETWORK_QUALITY_ESTIMATOR_H_