Style cleanup in preparation for auto-linting base/.

base/values_unittest.cc

Index: base/values_unittest.cc
diff --git a/base/values_unittest.cc b/base/values_unittest.cc
index 912b38025ef1d72f267c14fe46792b78ff8bf17b..fedfd09184daa72786f6977084552f625e13cb04 100644
--- a/base/values_unittest.cc
+++ b/base/values_unittest.cc
@@ -150,7 +150,7 @@ TEST(ValuesTest, StringValue) {
 // properly deleted by modifying the value of external flag on destruction.
 class DeletionTestValue : public Value {
  public:
-  DeletionTestValue(bool* deletion_flag) : Value(TYPE_NULL) {
+  explicit DeletionTestValue(bool* deletion_flag) : Value(TYPE_NULL) {
     Init(deletion_flag);  // Separate function so that we can use ASSERT_*
   }