Convert JsonWriter::Write to taking a const ref for the in-param

sync/test/fake_server/fake_server_verifier.cc

Index: sync/test/fake_server/fake_server_verifier.cc
diff --git a/sync/test/fake_server/fake_server_verifier.cc b/sync/test/fake_server/fake_server_verifier.cc
index bc645504cfe9c135f1340ca538cbdbb687648ac0..b968d0f919a06c9775d66e8fbf9a9fdf6bf1b7d5 100644
--- a/sync/test/fake_server/fake_server_verifier.cc
+++ b/sync/test/fake_server/fake_server_verifier.cc
@@ -53,8 +53,7 @@ AssertionResult VerifySessionsHierarchyEquality(
 string ConvertFakeServerContentsToString(
     const base::DictionaryValue& entities) {
   string entities_str;
-  if (!JSONWriter::WriteWithOptions(&entities,
-                                    JSONWriter::OPTIONS_PRETTY_PRINT,
+  if (!JSONWriter::WriteWithOptions(entities, JSONWriter::OPTIONS_PRETTY_PRINT,
                                     &entities_str)) {
     entities_str = "Could not convert FakeServer contents to string.";
   }