ART: Fix tidy warnings

Switch to char versions of find variants.

Add "explicit" constructor variants or refactor and
remove defaults.

Use const references.

Bug: 32619234
Test: m test-art-host
Change-Id: I970cc2f47d6cf8f0c74104b994b075b2fafb3d45
diff --git a/runtime/plugin.h b/runtime/plugin.h
index 18f3977..f077aaf 100644
--- a/runtime/plugin.h
+++ b/runtime/plugin.h
@@ -34,7 +34,7 @@
 // single-threaded fashion so not much need
 class Plugin {
  public:
-  static Plugin Create(std::string lib) {
+  static Plugin Create(const std::string& lib) {
     return Plugin(lib);
   }
 
@@ -66,7 +66,7 @@
   }
 
  private:
-  explicit Plugin(std::string library) : library_(library), dlopen_handle_(nullptr) { }
+  explicit Plugin(const std::string& library) : library_(library), dlopen_handle_(nullptr) { }
 
   std::string library_;
   void* dlopen_handle_;