Allow trailing comma in JSON policy files.

base/json/json_value_serializer.h

Index: base/json/json_value_serializer.h
diff --git a/base/json/json_value_serializer.h b/base/json/json_value_serializer.h
index 650008ec235aab6d356098b7c8c5bde0c1f7b224..21ec37a89d2087a46324d5f61dca8cc1efbfa4e8 100644
--- a/base/json/json_value_serializer.h
+++ b/base/json/json_value_serializer.h
@@ -74,7 +74,8 @@ class BASE_EXPORT JSONFileValueSerializer : public base::ValueSerializer {
   // When deserializing, the file should exist, but when serializing, the
   // serializer will attempt to create the file at the specified location.
   explicit JSONFileValueSerializer(const FilePath& json_file_path)
-    : json_file_path_(json_file_path) {}
+    : json_file_path_(json_file_path),
+      allow_trailing_comma_(false) {}
 
   virtual ~JSONFileValueSerializer() {}
 
@@ -116,8 +117,13 @@ class BASE_EXPORT JSONFileValueSerializer : public base::ValueSerializer {
   // be a JsonFileError.
   static const char* GetErrorMessageForCode(int error_code);
 
+  void set_allow_trailing_comma(bool new_value) {
+    allow_trailing_comma_ = new_value;
+  }
+
  private:
   FilePath json_file_path_;
+  bool allow_trailing_comma_;
 
   // A wrapper for file_util::ReadFileToString which returns a non-zero
   // JsonFileError if there were file errors.