Use Android callback API to obtain cellular signal strength

net/android/cellular_signal_strength.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_ANDROID_CELLULAR_SIGNAL_STRENGTH_H_
 #define NET_ANDROID_CELLULAR_SIGNAL_STRENGTH_H_
 
 #include <jni.h>
 #include <stdint.h>
 
+#include "base/android/scoped_java_ref.h"
 #include "base/compiler_specific.h"
+#include "base/macros.h"
+#include "base/threading/thread_checker.h"
 #include "net/base/net_export.h"
 
 namespace net {
 
 namespace android {
 
-namespace cellular_signal_strength {
+class NET_EXPORT_PRIVATE CellularSignalStrength {
+ public:
+  CellularSignalStrength();
 
-// Returns true if the signal strength (in dbM) of the currently registered
-// cellular connection is available, and sets |*signal_strength_dbm| to that
-// value.
-NET_EXPORT bool GetSignalStrengthDbm(int32_t* signal_strength_dbm)
-    WARN_UNUSED_RESULT;
+  ~CellularSignalStrength();
 
-// Returns true if the signal strength level (between 0 and 4, both inclusive)
-// of the currently registered cellular connection is available, and sets
-// |*signal_strength_level| to that value with lower value indicating lower
-// signal strength.
-NET_EXPORT bool GetSignalStrengthLevel(int32_t* signal_strength_level)
-    WARN_UNUSED_RESULT;
+  // Returns true if the signal strength level (between 0 and 4, both inclusive)
+  // of the currently registered cellular connection is available, and sets
+  // |*signal_strength_level| to that value with lower value indicating lower
+  // signal strength.
+  bool GetSignalStrengthLevel(int32_t* signal_strength_level) const

[RyanSturm, 2017/03/22 21:51:08]

nit: Could be a base::optional.

[tbansal1, 2017/03/23 18:28:53]

Done.

+      WARN_UNUSED_RESULT;
 
-}  // namespace cellular_signal_strength
+ private:
+  base::android::ScopedJavaGlobalRef<jobject> j_cellular_signal_strength_;
+
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(CellularSignalStrength);
+};
 
 }  // namespace android
 
 }  // namespace net
 
 #endif  // NET_ANDROID_CELLULAR_SIGNAL_STRENGTH_H_