buffet: Fix return type of DeviceRegistrationInfo::GetDeviceInfo

Result can't be any Value. According doc string it's a JSON object
which is DictionaryValue.

BUG=none
TEST=compile

Change-Id: I0988d4558629974ad1fc980a5e096319620b585c
Reviewed-on: https://chromium-review.googlesource.com/259660
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
Tested-by: Vitaly Buka <vitalybuka@chromium.org>

buffet/device_registration_info.cc

diff --git a/buffet/device_registration_info.cc b/buffet/device_registration_info.cc
index 9036ed8..ff4df89 100644
--- a/buffet/device_registration_info.cc
+++ b/buffet/device_registration_info.cc
@@ -460,10 +460,10 @@
   return resource;
 }
 
-std::unique_ptr<base::Value> DeviceRegistrationInfo::GetDeviceInfo(
+std::unique_ptr<base::DictionaryValue> DeviceRegistrationInfo::GetDeviceInfo(
     chromeos::ErrorPtr* error) {
   if (!CheckRegistration(error))
-    return std::unique_ptr<base::Value>();
+    return std::unique_ptr<base::DictionaryValue>();
 
   // TODO(antonm): Switch to DoCloudRequest later.
   auto response = chromeos::http::GetAndBlock(
@@ -476,10 +476,10 @@
       LOG(WARNING) << "Failed to retrieve the device info. Response code = "
                    << status_code;
       ParseGCDError(json.get(), error);
-      return std::unique_ptr<base::Value>();
+      return std::unique_ptr<base::DictionaryValue>();
     }
   }
-  return std::unique_ptr<base::Value>(json.release());
+  return json;
 }
 
 std::string DeviceRegistrationInfo::RegisterDevice(

buffet/device_registration_info.h

diff --git a/buffet/device_registration_info.h b/buffet/device_registration_info.h
index 7d64d31..e8f02eb 100644
--- a/buffet/device_registration_info.h
+++ b/buffet/device_registration_info.h
@@ -24,7 +24,7 @@
 #include "buffet/xmpp/xmpp_client.h"
 
 namespace base {
-class Value;
+class DictionaryValue;
 }  // namespace base
 
 namespace chromeos {
@@ -112,7 +112,8 @@
 
   // Gets the full device description JSON object, or nullptr if
   // the device is not registered or communication failure.
-  std::unique_ptr<base::Value> GetDeviceInfo(chromeos::ErrorPtr* error);
+  std::unique_ptr<base::DictionaryValue> GetDeviceInfo(
+      chromeos::ErrorPtr* error);
 
   // Registers the device.
   //