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/include/drm/DrmConstraints.h b/include/drm/DrmConstraints.h
index a9ec942..b8bb24f 100644
--- a/include/drm/DrmConstraints.h
+++ b/include/drm/DrmConstraints.h
@@ -70,7 +70,7 @@
     class KeyIterator {
         friend class DrmConstraints;
     private:
-        KeyIterator(DrmConstraints* drmConstraints)
+        explicit KeyIterator(DrmConstraints* drmConstraints)
             : mDrmConstraints(drmConstraints), mIndex(0) {}
 
     public:
@@ -93,7 +93,7 @@
     class Iterator {
         friend class DrmConstraints;
     private:
-        Iterator(DrmConstraints* drmConstraints)
+        explicit Iterator(DrmConstraints* drmConstraints)
             : mDrmConstraints(drmConstraints), mIndex(0) {}
 
     public:
diff --git a/include/drm/DrmInfo.h b/include/drm/DrmInfo.h
index 7b48541..53dfd61 100644
--- a/include/drm/DrmInfo.h
+++ b/include/drm/DrmInfo.h
@@ -55,7 +55,7 @@
         friend class DrmInfo;
 
     private:
-        KeyIterator(const DrmInfo* drmInfo)
+        explicit KeyIterator(const DrmInfo* drmInfo)
             : mDrmInfo(const_cast <DrmInfo*> (drmInfo)), mIndex(0) {}
 
     public:
@@ -79,7 +79,7 @@
         friend class DrmInfo;
 
     private:
-        Iterator(const DrmInfo* drmInfo)
+        explicit Iterator(const DrmInfo* drmInfo)
             : mDrmInfo(const_cast <DrmInfo*> (drmInfo)), mIndex(0) {}
 
     public:
diff --git a/include/drm/DrmInfoEvent.h b/include/drm/DrmInfoEvent.h
index dfca228..3165f02 100644
--- a/include/drm/DrmInfoEvent.h
+++ b/include/drm/DrmInfoEvent.h
@@ -77,7 +77,7 @@
      * @param[in] infoType Type of information
      * @param[in] message Message description
      */
-    DrmInfoEvent(int uniqueId, int infoType, const String8 message);
+    DrmInfoEvent(int uniqueId, int infoType, const String8& message);
 
     /**
      * Destructor for DrmInfoEvent
diff --git a/include/drm/DrmInfoRequest.h b/include/drm/DrmInfoRequest.h
index 3e48ecc..e2da4fe 100644
--- a/include/drm/DrmInfoRequest.h
+++ b/include/drm/DrmInfoRequest.h
@@ -69,7 +69,7 @@
         friend class DrmInfoRequest;
 
     private:
-        KeyIterator(const DrmInfoRequest* drmInfoRequest)
+        explicit KeyIterator(const DrmInfoRequest* drmInfoRequest)
             : mDrmInfoRequest(const_cast <DrmInfoRequest*> (drmInfoRequest)), mIndex(0) {}
 
     public:
@@ -93,7 +93,7 @@
         friend class DrmInfoRequest;
 
     private:
-        Iterator(const DrmInfoRequest* drmInfoRequest)
+        explicit Iterator(const DrmInfoRequest* drmInfoRequest)
             : mDrmInfoRequest(const_cast <DrmInfoRequest*> (drmInfoRequest)), mIndex(0) {}
 
     public:
diff --git a/include/drm/DrmMetadata.h b/include/drm/DrmMetadata.h
index 2c7538a..6624450 100644
--- a/include/drm/DrmMetadata.h
+++ b/include/drm/DrmMetadata.h
@@ -35,7 +35,7 @@
     class KeyIterator {
         friend class DrmMetadata;
     private:
-        KeyIterator(DrmMetadata* drmMetadata) : mDrmMetadata(drmMetadata), mIndex(0) {}
+        explicit KeyIterator(DrmMetadata* drmMetadata) : mDrmMetadata(drmMetadata), mIndex(0) {}
 
     public:
         KeyIterator(const KeyIterator& keyIterator);
@@ -57,7 +57,7 @@
     class Iterator {
         friend class DrmMetadata;
     private:
-        Iterator(DrmMetadata* drmMetadata) : mDrmMetadata(drmMetadata), mIndex(0) {}
+        explicit Iterator(DrmMetadata* drmMetadata) : mDrmMetadata(drmMetadata), mIndex(0) {}
 
     public:
         Iterator(const Iterator& iterator);
diff --git a/include/drm/DrmSupportInfo.h b/include/drm/DrmSupportInfo.h
index bf12b0b..bf85dbb 100644
--- a/include/drm/DrmSupportInfo.h
+++ b/include/drm/DrmSupportInfo.h
@@ -37,7 +37,7 @@
     class MimeTypeIterator {
         friend class DrmSupportInfo;
     private:
-        MimeTypeIterator(DrmSupportInfo* drmSupportInfo)
+        explicit MimeTypeIterator(DrmSupportInfo* drmSupportInfo)
            : mDrmSupportInfo(drmSupportInfo), mIndex(0) {}
     public:
         MimeTypeIterator(const MimeTypeIterator& iterator);
@@ -60,7 +60,7 @@
        friend class DrmSupportInfo;
 
     private:
-        FileSuffixIterator(DrmSupportInfo* drmSupportInfo)
+        explicit FileSuffixIterator(DrmSupportInfo* drmSupportInfo)
             : mDrmSupportInfo(drmSupportInfo), mIndex(0) {}
     public:
         FileSuffixIterator(const FileSuffixIterator& iterator);