base: Add three helper functions to Values API.

base/json/json_writer_unittest.cc

Index: base/json/json_writer_unittest.cc
diff --git a/base/json/json_writer_unittest.cc b/base/json/json_writer_unittest.cc
index 6d7714b5aad7fd4f964a2b5fa27839fbe18db51f..c14f1f5cd035e7237a85f6d58828859664879425 100644
--- a/base/json/json_writer_unittest.cc
+++ b/base/json/json_writer_unittest.cc
@@ -10,7 +10,7 @@ namespace base {
 
 TEST(JSONWriterTest, Writing) {
   // Test null
-  Value* root = Value::CreateNullValue();
+  Value* root = NullValue();
   std::string output_js;
   JSONWriter::Write(root, false, &output_js);
   ASSERT_EQ("null", output_js);
@@ -56,7 +56,7 @@ TEST(JSONWriterTest, Writing) {
   inner_dict->SetInteger("inner int", 10);
   ListValue* inner_list = new ListValue;
   list->Append(inner_list);
-  list->Append(Value::CreateBooleanValue(true));
+  list->Append(TrueValue());
 
   // Test the pretty-printer.
   JSONWriter::Write(&root_dict, false, &output_js);