CodeHealth: Remove use of DictionaryValue::empty in /ash/display

This change removes the use of DictionaryValue::empty()
and replaces with Value::DictEmpty()

This CL was uploaded by git cl split.

R=afakhry@chromium.org

Bug: 1187020
Change-Id: Ic557a205607118455834c5b638a55a58550764bb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2879647
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Auto-Submit: Fangzhen Song <songfangzhen@bytedance.com>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#880748}

ash/display/display_prefs.cc

@@ -675,7 +675,7 @@ void StoreDisplayTouchAssociations(PrefService* pref_service) {
           base::NumberToString(association_info.first),
           association_info_value->Clone());
     }
-    if (association_info_map_value.empty())
+    if (association_info_map_value.DictEmpty())
       continue;
 
     // Move the already serialized entry of AssociationInfoMap from

ash/display/display_prefs_unittest.cc

@@ -1564,7 +1564,7 @@ TEST_F(DisplayPrefsTest, DisplayMixedMirrorMode) {
   // Check the preferences.
   pref_data =
       local_state()->GetDictionary(prefs::kDisplayMixedMirrorModeParams);
-  EXPECT_TRUE(pref_data->empty());
+  EXPECT_TRUE(pref_data->DictEmpty());
 }
 
 }  // namespace ash