Fix google-explicit-constructor warnings in utils.

* Declare explicit conversion constructors.
* Use NOLINT(implicit) for implicit conversion constructors.

Bug: 28341362
Change-Id: I4fb58fa32aafc520b2ed862a05a8bdbfabbc6c35
Test: build with WITH_TIDY=1
diff --git a/include/utils/Thread.h b/include/utils/Thread.h
index 1532b7e..0f7ac9f 100644
--- a/include/utils/Thread.h
+++ b/include/utils/Thread.h
@@ -41,7 +41,7 @@
 public:
     // Create a Thread object, but doesn't create or start the associated
     // thread. See the run() method.
-                        Thread(bool canCallJava = true);
+    explicit            Thread(bool canCallJava = true);
     virtual             ~Thread();
 
     // Start the thread in threadLoop() which needs to be implemented.