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

printing/page_size_margins.cc

Index: printing/page_size_margins.cc
diff --git a/printing/page_size_margins.cc b/printing/page_size_margins.cc
index 8a6b48b6e6fb61d8952f0ecce37867cac1f76e3b..0f4d4fe8f93cabe5634e76349dd5d5115352518e 100644
--- a/printing/page_size_margins.cc
+++ b/printing/page_size_margins.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -12,7 +12,7 @@ namespace printing {
 
 void GetCustomMarginsFromJobSettings(const base::DictionaryValue& settings,
                                      PageSizeMargins* page_size_margins) {
-  DictionaryValue* custom_margins;
+  const DictionaryValue* custom_margins;
   if (!settings.GetDictionary(kSettingMarginsCustom, &custom_margins) ||
       !custom_margins->GetDouble(kSettingMarginTop,
                                  &page_size_margins->margin_top) ||