Correct const accessors in base/values.(h|cc), Part II (ListValue)

ash/system/network/tray_sms.cc

Index: ash/system/network/tray_sms.cc
diff --git a/ash/system/network/tray_sms.cc b/ash/system/network/tray_sms.cc
index f1714b892f93b7ca272f7e8274902071eef323ec..3e3f7c48df5bb36c51951ed98cffed63a2382bc2 100644
--- a/ash/system/network/tray_sms.cc
+++ b/ash/system/network/tray_sms.cc
@@ -209,7 +209,7 @@ class TraySms::SmsDetailedView : public TrayDetailsView,
     const base::ListValue& messages = tray_->messages();
     scroll_content()->RemoveAllChildViews(true);
     for (size_t index = 0; index < messages.GetSize(); ++index) {
-      base::DictionaryValue* message = NULL;
+      const base::DictionaryValue* message = NULL;
       if (!messages.GetDictionary(index, &message)) {
         LOG(ERROR) << "SMS message not a dictionary at: " << index;
         continue;