Add missing 'explicit's on single-argument constructors.

Change-Id: I1494df6e74ec16238971fb4346ba184eb61c37ab
diff --git a/src/timing_logger.h b/src/timing_logger.h
index f91b830..b60c60a 100644
--- a/src/timing_logger.h
+++ b/src/timing_logger.h
@@ -29,7 +29,7 @@
 
 class TimingLogger {
 public:
-  TimingLogger(const char* name) : name_(name) {
+  explicit TimingLogger(const char* name) : name_(name) {
     AddSplit("");
   }