Use Android callback API to obtain cellular signal strength

net/android/cellular_signal_strength.cc

Index: net/android/cellular_signal_strength.cc
diff --git a/net/android/cellular_signal_strength.cc b/net/android/cellular_signal_strength.cc
index 4c236954f7adab841bb53a4b363464eb5ab68c16..93fafaff129e06e1f98546905b1727f55ca9e0ef 100644
--- a/net/android/cellular_signal_strength.cc
+++ b/net/android/cellular_signal_strength.cc
@@ -11,7 +11,7 @@ namespace net {
 
 namespace android {
 
-namespace cellular_signal_strength {
+namespace {
 
 // GENERATED_JAVA_ENUM_PACKAGE: org.chromium.net
 enum CellularSignalStrengthError {
@@ -26,32 +26,30 @@ static_assert(
     INT32_MIN == ERROR_NOT_SUPPORTED,
     "CellularSignalStrengthError.ERROR_NOT_SUPPORTED has unexpected value");
 
-bool GetSignalStrengthDbm(int32_t* signal_strength_dbm) {
-  int32_t signal_strength_dbm_tmp =
-      Java_AndroidCellularSignalStrength_getSignalStrengthDbm(
-          base::android::AttachCurrentThread(),
-          base::android::GetApplicationContext());
-  if (signal_strength_dbm_tmp == ERROR_NOT_SUPPORTED)
-    return false;
+}  // namespace
 
-  *signal_strength_dbm = signal_strength_dbm_tmp;
-  return true;
+CellularSignalStrength::CellularSignalStrength() {
+  j_cellular_signal_strength_.Reset(Java_AndroidCellularSignalStrength_create(
+      base::android::AttachCurrentThread(),
+      base::android::GetApplicationContext()));

[pauljensen, 2017/04/13 11:36:30]

does this need to be called on the UI thread? if so please add
DCHECK(base::MessageLoopForUI::IsCurrent());

[tbansal1, 2017/06/07 21:39:20]

No, it does not have to be called on UI thread.
AndroidCellularSignalStrength.java explicitly creates a listener on UI thread.
This allows the rest of the code to run on non-UI threads.

 }
 
-bool GetSignalStrengthLevel(int32_t* signal_strength_level) {
-  int32_t signal_strength_level_tmp =
+CellularSignalStrength::~CellularSignalStrength() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+}
+
+base::Optional<int32_t> CellularSignalStrength::GetSignalStrengthLevel() const {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  int32_t signal_strength_level =
       Java_AndroidCellularSignalStrength_getSignalStrengthLevel(
-          base::android::AttachCurrentThread(),
-          base::android::GetApplicationContext());
-  if (signal_strength_level_tmp == ERROR_NOT_SUPPORTED)
-    return false;
+          base::android::AttachCurrentThread(), j_cellular_signal_strength_);
+  if (signal_strength_level == ERROR_NOT_SUPPORTED)
+    return base::Optional<int32_t>();
 
-  *signal_strength_level = signal_strength_level_tmp;
-  return true;
+  return signal_strength_level;
 }
 
-}  // namespace cellular_signal_strength
-
 }  // namespace android
 
 }  // namespace net