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

net/nqe/network_quality_estimator.h

Index: net/nqe/network_quality_estimator.h
diff --git a/net/nqe/network_quality_estimator.h b/net/nqe/network_quality_estimator.h
index afeca4eb01e1220879cb01bf87a644ebe06a9775..c5e31a70ba67e10c0db993e2028e1c89233aa170 100644
--- a/net/nqe/network_quality_estimator.h
+++ b/net/nqe/network_quality_estimator.h
@@ -10,7 +10,6 @@
 #include <map>
 #include <memory>
 #include <string>
-#include <tuple>
 
 #include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
@@ -24,9 +23,11 @@
 #include "net/base/network_change_notifier.h"
 #include "net/nqe/cached_network_quality.h"
 #include "net/nqe/external_estimate_provider.h"
+#include "net/nqe/network_id.h"
 #include "net/nqe/network_quality.h"
 #include "net/nqe/network_quality_observation.h"
 #include "net/nqe/network_quality_observation_source.h"
+#include "net/nqe/network_quality_store.h"
 #include "net/nqe/observation_buffer.h"
 #include "net/socket/socket_performance_watcher_factory.h"
 
@@ -238,46 +239,6 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   void SetUseSmallResponsesForTesting(bool use_small_responses);
 
  protected:
-  // 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.
-    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;
-  };
-
-  // Returns true if the cached network quality estimate was successfully read.
-  bool ReadCachedNetworkQualityEstimate();
-
   // NetworkChangeNotifier::ConnectionTypeObserver implementation:
   void OnConnectionTypeChanged(
       NetworkChangeNotifier::ConnectionType type) override;
@@ -352,9 +313,6 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
                            ObtainAlgorithmToUseFromParams);
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, HalfLifeParam);
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, ComputedPercentiles);
-  FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, TestCaching);
-  FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest,
-                           TestLRUCacheMaximumSize);
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest, TestGetMetricsSince);
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest,
                            TestExternalEstimateProviderMergeEstimates);
@@ -368,12 +326,6 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   typedef nqe::internal::Observation<int32_t> ThroughputObservation;
   typedef nqe::internal::ObservationBuffer<int32_t> ThroughputObservationBuffer;
 
-  // This does not use a unordered_map or hash_map for code simplicity (key just
-  // implements operator<, rather than hash and equality) and because the map is
-  // tiny.
-  typedef std::map<NetworkID, nqe::internal::CachedNetworkQuality>
-      CachedNetworkQualities;
-
   // Algorithms supported by network quality estimator for computing effective
   // connection type.
   enum class EffectiveConnectionTypeAlgorithm {
@@ -416,11 +368,6 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   // kilobits per second) values.
   static const int kMinimumThroughputVariationParameterKbps = 1;
 
-  // Maximum size of the cache that holds network quality estimates.
-  // Smaller size may reduce the cache hit rate due to frequent evictions.
-  // Larger size may affect performance.
-  static const size_t kMaximumNetworkQualityCacheSize = 10;
-
   // Returns the RTT value to be used when the valid RTT is unavailable. Readers
   // should discard RTT if it is set to the value returned by |InvalidRTT()|.
   static const base::TimeDelta InvalidRTT();
@@ -475,10 +422,7 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
 
   // Returns the current network ID checking by calling the platform APIs.
   // Virtualized for testing.
-  virtual NetworkID GetCurrentNetworkID() const;
-
-  // Writes the estimated quality of the current network to the cache.
-  void CacheNetworkQualityEstimate();
+  virtual nqe::internal::NetworkID GetCurrentNetworkID() const;
 
   void NotifyObserversOfRTT(const RttObservation& observation);
 
@@ -534,6 +478,9 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   void RecordExternalEstimateProviderMetrics(
       NQEExternalEstimateProviderStatus status) const;
 
+  // Returns true if the cached network quality estimate was successfully read.
+  bool ReadCachedNetworkQualityEstimate();
+
   // Determines if the requests to local host can be used in estimating the
   // network quality. Set to true only for tests.
   bool use_localhost_requests_;
@@ -570,7 +517,7 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   base::TimeTicks last_connection_change_;
 
   // ID of the current network.
-  NetworkID current_network_id_;
+  nqe::internal::NetworkID current_network_id_;
 
   // Peak network quality (fastest round-trip-time (RTT) and highest
   // downstream throughput) measured since last connectivity change. RTT is
@@ -580,9 +527,6 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   // 2) Includes server processing time.
   nqe::internal::NetworkQuality peak_network_quality_;
 
-  // Cache that stores quality of previously seen networks.
-  CachedNetworkQualities cached_network_qualities_;
-
   // Buffer that holds throughput observations (in kilobits per second) sorted
   // by timestamp.
   ThroughputObservationBuffer downstream_throughput_kbps_observations_;
@@ -642,6 +586,9 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   int32_t min_signal_strength_since_connection_change_;
   int32_t max_signal_strength_since_connection_change_;
 
+  // Stores the qualities of different networks.
+  nqe::internal::NetworkQualityStore network_quality_store_;
+
   base::ThreadChecker thread_checker_;
 
   base::WeakPtrFactory<NetworkQualityEstimator> weak_ptr_factory_;