Check and clear date cache in DateCurrentTime, DateLocalTimezone and getTimezoneOffset.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index 754f743f8cbeead5db1fe1e4e3db42b3949ef4ea..d7fa120cf835e052f7721cdd389f8481baf21592 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -9620,6 +9620,7 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_DateCurrentTime) {
   // time is milliseconds. Therefore, we floor the result of getting
   // the OS time.
   double millis = std::floor(OS::TimeCurrentMillis());
+  isolate->date_cache()->CheckTimezone();
   return isolate->heap()->NumberFromDouble(millis);
 }
 
@@ -9666,6 +9667,7 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_DateLocalTimezone) {
   ASSERT(args.length() == 1);
 
   CONVERT_DOUBLE_ARG_CHECKED(x, 0);
+  isolate->date_cache()->CheckTimezone();
   int64_t time = isolate->date_cache()->EquivalentTime(static_cast<int64_t>(x));
   const char* zone = OS::LocalTimezone(static_cast<double>(time));
   return isolate->heap()->AllocateStringFromUtf8(CStrVector(zone));