Fix clang-tidy warnings in drm.

* Add explicit keyword to conversion constructors.
Bug: 28341362
* Use const reference type for read-only parameters.
Bug: 30407689
* Use const reference type to avoid unnecessary copy.
Bug: 30413862
Test: build with WITH_TIDY=1

Change-Id: Idf1c48d7bfe3f0da20401cb3ff1983ec00be170d
diff --git a/media/libmediaplayerservice/Drm.cpp b/media/libmediaplayerservice/Drm.cpp
index b9cfe80..9dea492 100644
--- a/media/libmediaplayerservice/Drm.cpp
+++ b/media/libmediaplayerservice/Drm.cpp
@@ -62,7 +62,7 @@
 }
 
 struct DrmSessionClient : public DrmSessionClientInterface {
-    DrmSessionClient(Drm* drm) : mDrm(drm) {}
+    explicit DrmSessionClient(Drm* drm) : mDrm(drm) {}
 
     virtual bool reclaimSession(const Vector<uint8_t>& sessionId) {
         sp<Drm> drm = mDrm.promote();
diff --git a/media/libmediaplayerservice/DrmSessionManager.cpp b/media/libmediaplayerservice/DrmSessionManager.cpp
index 641f881..c934418 100644
--- a/media/libmediaplayerservice/DrmSessionManager.cpp
+++ b/media/libmediaplayerservice/DrmSessionManager.cpp
@@ -66,7 +66,7 @@
 DrmSessionManager::~DrmSessionManager() {}
 
 void DrmSessionManager::addSession(
-        int pid, sp<DrmSessionClientInterface> drm, const Vector<uint8_t> &sessionId) {
+        int pid, const sp<DrmSessionClientInterface>& drm, const Vector<uint8_t> &sessionId) {
     ALOGV("addSession(pid %d, drm %p, sessionId %s)", pid, drm.get(),
             GetSessionIdString(sessionId).string());
 
@@ -117,7 +117,7 @@
     }
 }
 
-void DrmSessionManager::removeDrm(sp<DrmSessionClientInterface> drm) {
+void DrmSessionManager::removeDrm(const sp<DrmSessionClientInterface>& drm) {
     ALOGV("removeDrm(%p)", drm.get());
 
     Mutex::Autolock lock(mLock);
diff --git a/media/libmediaplayerservice/DrmSessionManager.h b/media/libmediaplayerservice/DrmSessionManager.h
index ba5c268..ba27199 100644
--- a/media/libmediaplayerservice/DrmSessionManager.h
+++ b/media/libmediaplayerservice/DrmSessionManager.h
@@ -45,12 +45,12 @@
     static sp<DrmSessionManager> Instance();
 
     DrmSessionManager();
-    DrmSessionManager(sp<ProcessInfoInterface> processInfo);
+    explicit DrmSessionManager(sp<ProcessInfoInterface> processInfo);
 
-    void addSession(int pid, sp<DrmSessionClientInterface> drm, const Vector<uint8_t>& sessionId);
+    void addSession(int pid, const sp<DrmSessionClientInterface>& drm, const Vector<uint8_t>& sessionId);
     void useSession(const Vector<uint8_t>& sessionId);
     void removeSession(const Vector<uint8_t>& sessionId);
-    void removeDrm(sp<DrmSessionClientInterface> drm);
+    void removeDrm(const sp<DrmSessionClientInterface>& drm);
     bool reclaimSession(int callingPid);
 
 protected: