Serializer: Cache FlagList::Hash result.

test/cctest/test-serialize.cc

Index: test/cctest/test-serialize.cc
diff --git a/test/cctest/test-serialize.cc b/test/cctest/test-serialize.cc
index 71e5d82181d59183a4e53283b19977a2fddf61b3..88711b842940447358be689ab52d0f9b71f263f3 100644
--- a/test/cctest/test-serialize.cc
+++ b/test/cctest/test-serialize.cc
@@ -1372,7 +1372,9 @@ TEST(SerializeToplevelFlagChange) {
   v8::ScriptCompiler::CachedData* cache = ProduceCache(source);
 
   v8::Isolate* isolate2 = v8::Isolate::New();
+
   FLAG_allow_natives_syntax = true;  // Flag change should trigger cache reject.
+  FlagList::EnforceFlagImplications();
   {
     v8::Isolate::Scope iscope(isolate2);
     v8::HandleScope scope(isolate2);