audio policy: add method to query dB attenuation for a certain volume and device

Bug: 62492975
Test: Check dB value returned to AudioService when stream volume is
changed

Change-Id: I8d0a945e9151d230b93634e4b9e57bab68f44fa8
diff --git a/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp b/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp
index 1e63a05..8a2f1dc 100644
--- a/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp
+++ b/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp
@@ -769,4 +769,16 @@
     return mAudioPolicyManager->getMasterMono(mono);
 }
 
+
+float AudioPolicyService::getStreamVolumeDB(
+            audio_stream_type_t stream, int index, audio_devices_t device)
+{
+    if (mAudioPolicyManager == NULL) {
+        return NAN;
+    }
+    Mutex::Autolock _l(mLock);
+    return mAudioPolicyManager->getStreamVolumeDB(stream, index, device);
+}
+
+
 }; // namespace android
diff --git a/services/audiopolicy/service/AudioPolicyService.h b/services/audiopolicy/service/AudioPolicyService.h
index 9a083f4..2cd26ac 100644
--- a/services/audiopolicy/service/AudioPolicyService.h
+++ b/services/audiopolicy/service/AudioPolicyService.h
@@ -202,6 +202,9 @@
     virtual status_t setMasterMono(bool mono);
     virtual status_t getMasterMono(bool *mono);
 
+    virtual float    getStreamVolumeDB(
+                audio_stream_type_t stream, int index, audio_devices_t device);
+
             status_t doStopOutput(audio_io_handle_t output,
                                   audio_stream_type_t stream,
                                   audio_session_t session);