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

net/nqe/network_quality_observation_source.h

 // 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_QUALITY_OBSERVATION_SOURCE_H_
 #define NET_NQE_NETWORK_QUALITY_OBSERVATION_SOURCE_H_
 
 namespace net {
 
 // On Android, a Java counterpart will be generated for this enum.
@@ skipping 14 matching lines @@
 
   // The observation is a previously cached estimate of the metric.
   NETWORK_QUALITY_OBSERVATION_SOURCE_CACHED_ESTIMATE,
 
   // The observation is derived from network connection information provided
   // by the platform. For example, typical RTT and throughput values are used
   // for a given type of network connection.
   NETWORK_QUALITY_OBSERVATION_SOURCE_DEFAULT_FROM_PLATFORM,
 
   // The observation came from a Chromium-external source.
-  NETWORK_QUALITY_OBSERVATION_SOURCE_EXTERNAL_ESTIMATE
+  NETWORK_QUALITY_OBSERVATION_SOURCE_EXTERNAL_ESTIMATE,
+
+  NETWORK_QUALITY_OBSERVATION_SOURCE_MAX,
 };
 
 }  // namespace net
 
 #endif  // NET_NQE_NETWORK_QUALITY_OBSERVATION_SOURCE_H_