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/AudioPolicyInterface.h b/services/audiopolicy/AudioPolicyInterface.h
index d987469..a1221fc 100644
--- a/services/audiopolicy/AudioPolicyInterface.h
+++ b/services/audiopolicy/AudioPolicyInterface.h
@@ -231,7 +231,7 @@
 
     virtual status_t releaseSoundTriggerSession(audio_session_t session) = 0;
 
-    virtual status_t registerPolicyMixes(Vector<AudioMix> mixes) = 0;
+    virtual status_t registerPolicyMixes(const Vector<AudioMix>& mixes) = 0;
     virtual status_t unregisterPolicyMixes(Vector<AudioMix> mixes) = 0;
 
     virtual status_t startAudioSource(const struct audio_port_config *source,