Correct const accessors in base/values.(h|cc)

chrome/test/webdriver/commands/command.cc

Index: chrome/test/webdriver/commands/command.cc
diff --git a/chrome/test/webdriver/commands/command.cc b/chrome/test/webdriver/commands/command.cc
index 7f4686de4e34f7317c67a26dd9d6aa3c36ce87f6..61770b72bbc73bb55765af6feaf5a9a7ae5579ca 100644
--- a/chrome/test/webdriver/commands/command.cc
+++ b/chrome/test/webdriver/commands/command.cc
@@ -40,7 +40,7 @@ bool Command::HasParameter(const std::string& key) const {
 }
 
 bool Command::IsNullParameter(const std::string& key) const {
-  Value* value;
+  const Value* value;
   return parameters_.get() &&
          parameters_->Get(key, &value) &&
          value->IsType(Value::TYPE_NULL);
@@ -76,12 +76,12 @@ bool Command::GetDoubleParameter(const std::string& key, double* out) const {
 }
 
 bool Command::GetDictionaryParameter(const std::string& key,
-                                     DictionaryValue** out) const {
+                                     const DictionaryValue** out) const {
   return parameters_.get() != NULL && parameters_->GetDictionary(key, out);
 }
 
 bool Command::GetListParameter(const std::string& key,
-                               ListValue** out) const {
+                               const ListValue** out) const {
   return parameters_.get() != NULL && parameters_->GetList(key, out);
 }