Expose cellular signal strength on Android to native

net/android/cellular_signal_strength.cc

+// 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.
+
+#include "net/android/cellular_signal_strength.h"
+
+#include "base/android/context_utils.h"
+#include "jni/AndroidCellularSignalStrength_jni.h"
+
+namespace net {
+
+namespace android {
+
+namespace cellular_signal_strength {
+
+// GENERATED_JAVA_ENUM_PACKAGE: org.chromium.net
+enum CellularSignalStrengthError {
+  // Value returned by CellularSignalStrength APIs when a valid value is
+  // unavailable.
+  ERROR_NOT_SUPPORTED = -2147483648,

[bengr, 2016/06/10 20:57:37]

Why not just use INT32_MIN? Add a comment that doing so is incompatible with the
Java generation magic. You can add that comment just before the static_assert.

[tbansal1, 2016/06/16 00:58:01]

Done.

+};
+
+static_assert(
+    INT32_MIN == ERROR_NOT_SUPPORTED,
+    "CellularSignalStrengthError.ERROR_NOT_SUPPORTED has unexpected value");
+
+bool GetRssiDbm(int32_t* rssi) {
+  int32_t rssi_tmp = Java_AndroidCellularSignalStrength_getRssiDbm(

[bengr, 2016/06/10 20:57:37]

It might be better to avoid using the term RSSI and instead use
SignalStrengthDbm.

[tbansal1, 2016/06/16 00:58:01]

Done.

+      base::android::AttachCurrentThread(),
+      base::android::GetApplicationContext());
+  if (rssi_tmp == ERROR_NOT_SUPPORTED)
+    return false;
+
+  *rssi = rssi_tmp;

[bengr, 2016/06/10 20:57:37]

I don't like _tmp, but can't think of anything better. Maybe:

bool GetSignalStrengthDbm(int43_t* rssi_to_return) {
  int32_t rssi = whatever();
  ...
  *rssi_to_return = rssi;
  return true;
}

[tbansal1, 2016/06/16 00:58:02]

I would prefer not to put |rssi_to_return| in the function header which appears
in the .h and .cc file.

+  return true;
+}
+
+bool GetSignalLevel(int32_t* signal_level) {
+  int32_t signal_level_tmp = Java_AndroidCellularSignalStrength_getSignalLevel(
+      base::android::AttachCurrentThread(),
+      base::android::GetApplicationContext());
+  if (signal_level_tmp == ERROR_NOT_SUPPORTED)
+    return false;
+
+  *signal_level = signal_level_tmp;
+  return true;
+}
+
+bool Register(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+}  // namespace cellular_signal_strength
+
+}  // namespace android
+
+}  // namespace net