[date] Refactor the %_DateField intrinsic to be optimizable.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 8beee140e9b631ffe75ac4cee149a6f36a82aa4d..7e6181ecade0854a7bc308ad81d5e8e017859cfd 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -2875,9 +2875,10 @@ class HCheckInstanceType final : public HUnaryOperation {
   enum Check {
     IS_SPEC_OBJECT,
     IS_JS_ARRAY,
+    IS_JS_DATE,
     IS_STRING,
     IS_INTERNALIZED_STRING,
-    LAST_INTERVAL_CHECK = IS_JS_ARRAY
+    LAST_INTERVAL_CHECK = IS_JS_DATE
   };
 
   DECLARE_INSTRUCTION_FACTORY_P2(HCheckInstanceType, HValue*, Check);
@@ -2892,6 +2893,8 @@ class HCheckInstanceType final : public HUnaryOperation {
     switch (check_) {
       case IS_SPEC_OBJECT: return HType::JSObject();
       case IS_JS_ARRAY: return HType::JSArray();
+      case IS_JS_DATE:
+        return HType::JSObject();
       case IS_STRING: return HType::String();
       case IS_INTERNALIZED_STRING: return HType::String();
     }