Fix clang-tidy warnings in audio and playerservice.

* Add explicit keyword to conversion constructors.
Bug: 28341362
* Use const reference type for read-only parameters.
Bug: 30407689
Test: build with WITH_TIDY=1

Change-Id: I265f3b094e08d5705b506b3fbba51439c134af84
Merged-In: I265f3b094e08d5705b506b3fbba51439c134af84
diff --git a/services/audiopolicy/service/AudioPolicyInterfaceImplLegacy.cpp b/services/audiopolicy/service/AudioPolicyInterfaceImplLegacy.cpp
index 13af3ef..f044e37 100644
--- a/services/audiopolicy/service/AudioPolicyInterfaceImplLegacy.cpp
+++ b/services/audiopolicy/service/AudioPolicyInterfaceImplLegacy.cpp
@@ -601,7 +601,7 @@
     return INVALID_OPERATION;
 }
 
-status_t AudioPolicyService::registerPolicyMixes(Vector<AudioMix> mixes __unused,
+status_t AudioPolicyService::registerPolicyMixes(const Vector<AudioMix>& mixes __unused,
                                                  bool registration __unused)
 {
     return INVALID_OPERATION;