Use Android callback API to obtain cellular signal strength

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 19e460a5a5c35046030b61192e2b318ed358063c..7b2e1fa0d6746c864861efd6a34c66e187933880 100644
--- a/net/nqe/network_quality_estimator.h
+++ b/net/nqe/network_quality_estimator.h
@@ -38,6 +38,10 @@
 #include "net/nqe/rtt_throughput_estimates_observer.h"
 #include "net/socket/socket_performance_watcher_factory.h"
 
+#if defined(OS_ANDROID)
+#include "net/android/cellular_signal_strength.h"
+#endif  // OS_ANDROID
+
 namespace base {
 class TickClock;
 }  // namespace base
@@ -647,15 +651,15 @@ class NET_EXPORT NetworkQualityEstimator
   // |effective_connection_type_recomputation_interval_| ago).
   EffectiveConnectionType effective_connection_type_;
 
-  // Last known value of the wireless signal strength. Set to INT32_MIN if
-  // unavailable. |signal_strength_dbm_| is reset to INT32_MIN on connection
-  // change events.
-  int32_t signal_strength_dbm_;
+  // Last known value of the wireless signal strength level. If the signal
+  // strength level is available, the value is set to between 0 and 4, both
+  // inclusive. If the value is unavailable, |signal_strength_| has null value.
+  base::Optional<int32_t> signal_strength_;
 
-  // Minimum and maximum signal strength (in dBm) observed since last connection
+  // Minimum and maximum signal strength level observed since last connection
   // change. Updated on connection change and main frame requests.
-  int32_t min_signal_strength_since_connection_change_;
-  int32_t max_signal_strength_since_connection_change_;
+  base::Optional<int32_t> min_signal_strength_since_connection_change_;
+  base::Optional<int32_t> max_signal_strength_since_connection_change_;
 
   // Stores the qualities of different networks.
   std::unique_ptr<nqe::internal::NetworkQualityStore> network_quality_store_;
@@ -675,6 +679,12 @@ class NET_EXPORT NetworkQualityEstimator
   const std::vector<NetworkQualityObservationSource>
       disallowed_observation_sources_for_transport_;
 
+#if defined(OS_ANDROID)
+  // Initialized only if the experiment to use the cellular signal strength
+  // is enabled.
+  std::unique_ptr<android::CellularSignalStrength> cellular_signal_strength_;
+#endif  // OS_ANDROID
+
   base::WeakPtrFactory<NetworkQualityEstimator> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkQualityEstimator);