CodeHealth: Remove use of DictionaryValue::empty in /components/sync

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

This CL was uploaded by git cl split.

R=rushans@google.com

Bug: 1187020
Change-Id: Idc70cc8b70c8c3adbda45ae7b70808f89b651983
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2879652
Commit-Queue: Rushan Suleymanov <rushans@google.com>
Auto-Submit: Fangzhen Song <songfangzhen@bytedance.com>
Reviewed-by: Rushan Suleymanov <rushans@google.com>
Cr-Commit-Position: refs/heads/master@{#880742}

components/sync/js/js_event_details_unittest.cc

@@ -17,7 +17,7 @@ class JsEventDetailsTest : public testing::Test {};
 
 TEST_F(JsEventDetailsTest, EmptyList) {
   JsEventDetails details;
-  EXPECT_TRUE(details.Get().empty());
+  EXPECT_TRUE(details.Get().DictEmpty());
   EXPECT_EQ("{}", details.ToString());
 }
 
@@ -31,7 +31,7 @@ TEST_F(JsEventDetailsTest, FromDictionary) {
   JsEventDetails details(&dict);
 
   // |details| should take over |dict|'s data.
-  EXPECT_TRUE(dict.empty());
+  EXPECT_TRUE(dict.DictEmpty());
   EXPECT_TRUE(details.Get().Equals(&dict_copy));
 }