buffet: Use DictionaryValue in StorageInterface

It is used to store dictionaries only.

BUG=none
TEST='FEATURES=test emerge-gizmo buffet'

Change-Id: Ic85f77a3d31853bf8ed244d7f58264e9c809f666
Reviewed-on: https://chromium-review.googlesource.com/271301
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Vitaly Buka <vitalybuka@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
Tested-by: Vitaly Buka <vitalybuka@chromium.org>
diff --git a/buffet/utils.h b/buffet/utils.h
index 0325171..8e4bfd6 100644
--- a/buffet/utils.h
+++ b/buffet/utils.h
@@ -30,12 +30,14 @@
 // Helper function to load a JSON file that is expected to be
 // an object/dictionary. In case of error, returns empty unique ptr and fills
 // in error details in |error|.
-std::unique_ptr<const base::DictionaryValue> LoadJsonDict(
-    const base::FilePath& json_file_path, chromeos::ErrorPtr* error);
+std::unique_ptr<base::DictionaryValue> LoadJsonDict(
+    const base::FilePath& json_file_path,
+    chromeos::ErrorPtr* error);
 
 // Helper function to load a JSON dictionary from a string.
-std::unique_ptr<const base::DictionaryValue> LoadJsonDict(
-    const std::string& json_string, chromeos::ErrorPtr* error);
+std::unique_ptr<base::DictionaryValue> LoadJsonDict(
+    const std::string& json_string,
+    chromeos::ErrorPtr* error);
 
 // Synchronously resolves the |host| and connects a socket to the resolved
 // address/port.