[Metrics, Cleanup] Replace a misleading TODO with documentation.

components/metrics/net/network_metrics_provider.cc

 // Copyright 2014 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.
 
 #include "components/metrics/net/network_metrics_provider.h"
 
 #include <string>
 #include <vector>
 
 #include "base/compiler_specific.h"
@@ skipping 31 matching lines @@
 
 void NetworkMetricsProvider::ProvideSystemProfileMetrics(
     SystemProfileProto* system_profile) {
   SystemProfileProto::Network* network = system_profile->mutable_network();
   network->set_connection_type_is_ambiguous(connection_type_is_ambiguous_);
   network->set_connection_type(GetConnectionType());
   network->set_wifi_phy_layer_protocol_is_ambiguous(
       wifi_phy_layer_protocol_is_ambiguous_);
   network->set_wifi_phy_layer_protocol(GetWifiPHYLayerProtocol());
 
-  // Resets the "ambiguous" flags, since a new metrics log session has started.
+  // Update the connection type. Note that this is necessary to set the network
+  // type to "none" if there is no network connection for an entire UMA logging
+  // window, since OnConnectionTypeChanged() ignores transitions to the "none"
+  // state.
+  connection_type_ = net::NetworkChangeNotifier::GetConnectionType();
+  // Reset the "ambiguous" flags, since a new metrics log session has started.
   connection_type_is_ambiguous_ = false;
-  // TODO(isherman): This line seems unnecessary.
-  connection_type_ = net::NetworkChangeNotifier::GetConnectionType();
   wifi_phy_layer_protocol_is_ambiguous_ = false;
 
   if (!wifi_access_point_info_provider_.get()) {
 #if defined(OS_CHROMEOS)
     wifi_access_point_info_provider_.reset(
         new WifiAccessPointInfoProviderChromeos());
 #else
     wifi_access_point_info_provider_.reset(
         new WifiAccessPointInfoProvider());
 #endif  // OS_CHROMEOS
   }
 
   // Connected wifi access point information.
   WifiAccessPointInfoProvider::WifiAccessPointInfo info;
   if (wifi_access_point_info_provider_->GetInfo(&info))
     WriteWifiAccessPointProto(info, network);
 }
 
 void NetworkMetricsProvider::OnConnectionTypeChanged(
     net::NetworkChangeNotifier::ConnectionType type) {
+  // To avoid reporting an ambiguous connection type for users on flaky
+  // connections, ignore transitions to the "none" state. Note that the
+  // connection type is refreshed in ProvideSystemProfileMetrics() each time a
+  // new UMA logging window begins, so users who genuinely transition to offline
+  // mode for an extended duration will still be at least partially represented
+  // in the metrics logs.
   if (type == net::NetworkChangeNotifier::CONNECTION_NONE)
     return;
+
   if (type != connection_type_ &&
       connection_type_ != net::NetworkChangeNotifier::CONNECTION_NONE) {
     connection_type_is_ambiguous_ = true;
   }
   connection_type_ = type;
 
   ProbeWifiPHYLayerProtocol();
 }
 
 SystemProfileProto::Network::ConnectionType
@@ skipping 153 matching lines @@
 void NetworkMetricsProvider::GetIsCellularConnection(bool* is_cellular_out) {
   *is_cellular_out = IsCellularConnection();
 }
 
 base::Callback<void(bool*)> NetworkMetricsProvider::GetConnectionCallback() {
   return base::Bind(&NetworkMetricsProvider::GetIsCellularConnection,
                  weak_ptr_factory_.GetWeakPtr());
 }
 
 }  // namespace metrics