Fix clang-tidy warnings in mediaresourcemanager.

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

Change-Id: I9aac64b379ddb77a9abb4b03a6648f38e2a756ab
diff --git a/services/mediaresourcemanager/ServiceLog.h b/services/mediaresourcemanager/ServiceLog.h
index a6f16eb..380e86a 100644
--- a/services/mediaresourcemanager/ServiceLog.h
+++ b/services/mediaresourcemanager/ServiceLog.h
@@ -30,7 +30,7 @@
 class ServiceLog : public RefBase {
 public:
     ServiceLog();
-    ServiceLog(size_t maxNum);
+    explicit ServiceLog(size_t maxNum);
 
     void add(const String8 &log);
     String8 toString(const char *linePrefix = NULL) const;