Fix a bunch of lint.

There are still about 1800 lint warnings, so don't get too excited...

Change-Id: I2394bd6e750b94060231378b3a7a88b87f70c757
diff --git a/src/logging.h b/src/logging.h
index 585cc6d..94dd2c6 100644
--- a/src/logging.h
+++ b/src/logging.h
@@ -254,7 +254,7 @@
 template<typename T>
 class ToStr {
  public:
-  ToStr(const T& value) {
+  explicit ToStr(const T& value) {
     std::ostringstream os;
     os << value;
     s_ = os.str();