Add missing (and remove superfluous) 'explicit' from constructors.

base/values.cc

Index: base/values.cc
diff --git a/base/values.cc b/base/values.cc
index 459d56fa0222fa2ea98503ece9dd755022908725..efffc8942c7b9e905ef8eb9102c510f978976a31 100644
--- a/base/values.cc
+++ b/base/values.cc
@@ -68,7 +68,7 @@ class ValueEquals {
   // Pass the value against which all consecutive calls of the () operator will
   // compare their argument to. This Value object must not be destroyed while
   // the ValueEquals is  in use.
-  ValueEquals(const Value* first) : first_(first) { }
+  explicit ValueEquals(const Value* first) : first_(first) { }
 
   bool operator ()(const Value* second) const {
     return first_->Equals(second);