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/common/DrmInfoEvent.cpp b/drm/common/DrmInfoEvent.cpp
index 27a5a2d..703e363 100644
--- a/drm/common/DrmInfoEvent.cpp
+++ b/drm/common/DrmInfoEvent.cpp
@@ -19,7 +19,7 @@
 
 using namespace android;
 
-DrmInfoEvent::DrmInfoEvent(int uniqueId, int infoType, const String8 message)
+DrmInfoEvent::DrmInfoEvent(int uniqueId, int infoType, const String8 &message)
     : mUniqueId(uniqueId),
       mInfoType(infoType),
       mMessage(message) {