Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: Idadc9ad22fdd9d014c8fe0522c89b6ec9d05ae98
diff --git a/tests/binder_test.cpp b/tests/binder_test.cpp
index fd94d2e..9638230 100644
--- a/tests/binder_test.cpp
+++ b/tests/binder_test.cpp
@@ -104,7 +104,7 @@
 
 class TimedOperation : public Stopwatch {
 public:
-    TimedOperation(std::string name): mName(name) {}
+    explicit TimedOperation(const std::string &name): mName(name) {}
     virtual ~TimedOperation() {
         fprintf(stderr, "    %s: %6.1f ms\n", mName.c_str(), timeTaken());
     }