Add support to get registered policy mixes

This new (Test)Api exposes all AudioMixes registered with AudioPolicyManager.
The TestApi is very useful in verifying AudioMix/AudioPolicy behavior in
the Java and Native layer to debug and assert the correct behavior.

Bug: 309080867
Test: atest AudioHostTest

Change-Id: Icdc2a482228ab06ac7386915ddbeb0cfcc24889d
diff --git a/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp b/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp
index 6e1ecec..2a4c069 100644
--- a/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp
+++ b/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp
@@ -1810,6 +1810,23 @@
     }
 }
 
+Status
+AudioPolicyService::getRegisteredPolicyMixes(std::vector<::android::media::AudioMix>* mixesAidl) {
+    if (mAudioPolicyManager == nullptr) {
+        return binderStatusFromStatusT(NO_INIT);
+    }
+
+    std::vector<AudioMix> mixes;
+    int status = mAudioPolicyManager->getRegisteredPolicyMixes(mixes);
+
+    for (const auto& mix : mixes) {
+        media::AudioMix aidlMix = VALUE_OR_RETURN_BINDER_STATUS(legacy2aidl_AudioMix(mix));
+        mixesAidl->push_back(aidlMix);
+    }
+
+    return binderStatusFromStatusT(status);
+}
+
 Status AudioPolicyService::updatePolicyMixes(
         const ::std::vector<::android::media::AudioMixUpdate>& updates) {
     audio_utils::lock_guard _l(mMutex);