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 5c2718a12b6df2eb8ba4763a739942f511798982..a6ec07afacbbff52786aefa842a3d54198ca515c 100644
--- a/net/nqe/network_quality_estimator.h
+++ b/net/nqe/network_quality_estimator.h
@@ -34,6 +34,10 @@
 #include "net/nqe/observation_buffer.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
@@ -669,10 +673,10 @@ class NET_EXPORT NetworkQualityEstimator
   // The factor by which the weight of an observation reduces every second.
   const double weight_multiplier_per_second_;
 
-  // The factor by which the weight of an observation reduces for every dBm
-  // difference between the current signal strength (in dBm), and the signal
-  // strength at the time when the observation was taken.
-  const double weight_multiplier_per_dbm_;
+  // The factor by which the weight of an observation reduces for every signal
+  // strength level difference between the current signal strength, and the
+  // signal strength at the time when the observation was taken.
+  const double weight_multiplier_per_signal_strength_level_;
 
   // Algorithm to use for computing effective connection type. The value is
   // obtained from field trial parameters. If the value from field trial
@@ -786,15 +790,16 @@ 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. Set to INT32_MIN if
+  // unavailable. |signal_strength_| is reset to INT32_MIN on connection
+  // change events. If the signal strength level is available, the value is set
+  // to between 0 and 4, both inclusive.
+  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_;
 
   // It is costlier to add values to a sparse histogram. So, the correlation UMA
   // is recorded with |correlation_uma_logging_probability_| since recording it
@@ -830,6 +835,12 @@ 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);