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/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);