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/Mutex.h b/include/utils/Mutex.h
index f027c79..8b720b9 100644
--- a/include/utils/Mutex.h
+++ b/include/utils/Mutex.h
@@ -48,8 +48,8 @@
     };
 
                 Mutex();
-                Mutex(const char* name);
-                Mutex(int type, const char* name = NULL);
+    explicit    Mutex(const char* name);
+    explicit    Mutex(int type, const char* name = NULL);
                 ~Mutex();
 
     // lock or unlock the mutex
@@ -73,8 +73,8 @@
     // constructed and released when Autolock goes out of scope.
     class Autolock {
     public:
-        inline Autolock(Mutex& mutex) : mLock(mutex)  { mLock.lock(); }
-        inline Autolock(Mutex* mutex) : mLock(*mutex) { mLock.lock(); }
+        inline explicit Autolock(Mutex& mutex) : mLock(mutex)  { mLock.lock(); }
+        inline explicit Autolock(Mutex* mutex) : mLock(*mutex) { mLock.lock(); }
         inline ~Autolock() { mLock.unlock(); }
     private:
         Mutex& mLock;