Add a network quality cache observer

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 80c7feb6703eb7999e95c9db5e55583680abe5bb..0eb60b10960d8e971b28beb026798492eac14433 100644
--- a/net/nqe/network_quality_estimator.h
+++ b/net/nqe/network_quality_estimator.h
@@ -286,6 +286,9 @@ class NET_EXPORT NetworkQualityEstimator
   // Returns a random double in the range [0.0, 1.0). Virtualized for testing.
   virtual double RandDouble() const;
 
+  // Returns |network_quality_store_|. Used only for testing.
+  nqe::internal::NetworkQualityStore* NetworkQualityStoreForTesting() const;
+
  private:
   FRIEND_TEST_ALL_PREFIXES(NetworkQualityEstimatorTest,
                            AdaptiveRecomputationEffectiveConnectionType);
@@ -611,7 +614,7 @@ class NET_EXPORT NetworkQualityEstimator
   const double correlation_uma_logging_probability_;
 
   // Stores the qualities of different networks.
-  nqe::internal::NetworkQualityStore network_quality_store_;
+  std::unique_ptr<nqe::internal::NetworkQualityStore> network_quality_store_;
 
   base::ThreadChecker thread_checker_;