NQE: Add accuracy histogram for external estimate provider

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..23fc8f7cd4dc7e6c9085f14e5b2c4e8972b03cba 100644
--- a/net/nqe/network_quality_estimator.h
+++ b/net/nqe/network_quality_estimator.h
@@ -425,6 +425,10 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   // should discard RTT if it is set to the value returned by |InvalidRTT()|.
   static const base::TimeDelta InvalidRTT();
 
+  // Queries external estimate provider for network quality. When the network
+  // quality is available, OnUpdatedEstimateAvailable() is called.
+  void MaybeQueryExternalEstimateProvider() const;
+
   // Records UMA when there is a change in connection type.
   void RecordMetricsOnConnectionTypeChanged() const;
 
@@ -611,6 +615,10 @@ class NET_EXPORT_PRIVATE NetworkQualityEstimator
   nqe::internal::NetworkQuality estimated_quality_at_last_main_frame_;
   EffectiveConnectionType effective_connection_type_at_last_main_frame_;
 
+  // Estimated network quality obtained from external estimate provider when the
+  // external estimate provider was last queried.
+  nqe::internal::NetworkQuality external_estimate_provider_quality_;
+
   // ExternalEstimateProvider that provides network quality using operating
   // system APIs. May be NULL.
   const std::unique_ptr<ExternalEstimateProvider> external_estimate_provider_;