Fix google-explicit-constructor warnings in art.

* Add explicit keyword to conversion constructors,
  or NOLINT for implicit converters.
Bug: 28341362
Test: build with WITH_TIDY=1

Change-Id: I1e1ee2661812944904fedadeff97b620506db47d
diff --git a/runtime/base/transform_iterator.h b/runtime/base/transform_iterator.h
index 9c8f822..f1a8a52 100644
--- a/runtime/base/transform_iterator.h
+++ b/runtime/base/transform_iterator.h
@@ -62,7 +62,7 @@
       : data_(base, fn) { }
 
   template <typename OtherBI>
-  TransformIterator(const TransformIterator<OtherBI, Function>& other)
+  TransformIterator(const TransformIterator<OtherBI, Function>& other)  // NOLINT, implicit
       : data_(other.base(), other.GetFunction()) {
   }