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/drm/libdrmframework/include/IDrmManagerService.h b/drm/libdrmframework/include/IDrmManagerService.h
index fe55650..0376b49 100644
--- a/drm/libdrmframework/include/IDrmManagerService.h
+++ b/drm/libdrmframework/include/IDrmManagerService.h
@@ -169,7 +169,7 @@
 class BpDrmManagerService: public BpInterface<IDrmManagerService>
 {
 public:
-    BpDrmManagerService(const sp<IBinder>& impl)
+    explicit BpDrmManagerService(const sp<IBinder>& impl)
             : BpInterface<IDrmManagerService>(impl) {}
 
     virtual int addUniqueId(bool isNative);
diff --git a/drm/libdrmframework/include/IDrmServiceListener.h b/drm/libdrmframework/include/IDrmServiceListener.h
index 7f7109f..78c5d1a 100644
--- a/drm/libdrmframework/include/IDrmServiceListener.h
+++ b/drm/libdrmframework/include/IDrmServiceListener.h
@@ -49,7 +49,7 @@
 class BpDrmServiceListener: public BpInterface<IDrmServiceListener>
 {
 public:
-    BpDrmServiceListener(const sp<IBinder>& impl)
+    explicit BpDrmServiceListener(const sp<IBinder>& impl)
             : BpInterface<IDrmServiceListener>(impl) {}
 
     virtual status_t notify(const DrmInfoEvent& event);
diff --git a/drm/libdrmframework/plugins/forward-lock/FwdLockEngine/include/FwdLockEngine.h b/drm/libdrmframework/plugins/forward-lock/FwdLockEngine/include/FwdLockEngine.h
index a31b951..d222703 100644
--- a/drm/libdrmframework/plugins/forward-lock/FwdLockEngine/include/FwdLockEngine.h
+++ b/drm/libdrmframework/plugins/forward-lock/FwdLockEngine/include/FwdLockEngine.h
@@ -539,7 +539,7 @@
             offset = 0;
         }
 
-        DecodeSession(int fd) {
+        explicit DecodeSession(int fd) {
             fileDesc = fd;
             offset = 0;
         }