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
diff --git a/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp b/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp
index dc45a54..f6da920 100644
--- a/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp
+++ b/services/audiopolicy/service/AudioPolicyInterfaceImpl.cpp
@@ -694,7 +694,7 @@
     return mAudioPolicyManager->releaseSoundTriggerSession(session);
 }
 
-status_t AudioPolicyService::registerPolicyMixes(Vector<AudioMix> mixes, bool registration)
+status_t AudioPolicyService::registerPolicyMixes(const Vector<AudioMix>& mixes, bool registration)
 {
     Mutex::Autolock _l(mLock);
     if(!modifyAudioRoutingAllowed()) {