[runtime] Migrate several Date builtins to C++.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 9b235d5c7a64e258d5c770829e9021d56a953cad..bf40d54ba62bd3bebbd610270652f926ba9a09cc 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1967,6 +1967,10 @@ class JSReceiver: public HeapObject {
 // caching.
 class JSObject: public JSReceiver {
  public:
+  static MUST_USE_RESULT MaybeHandle<JSObject> New(
+      Handle<JSFunction> constructor, Handle<JSReceiver> new_target,
+      Handle<AllocationSite> site = Handle<AllocationSite>::null());
+
   // [properties]: Backing storage for properties.
   // properties is a FixedArray in the fast case and a Dictionary in the
   // slow case.
@@ -7530,6 +7534,10 @@ class DateCache;
 // Representation for JS date objects.
 class JSDate: public JSObject {
  public:
+  static MUST_USE_RESULT MaybeHandle<JSDate> New(Handle<JSFunction> constructor,
+                                                 Handle<JSReceiver> new_target,
+                                                 double tv);
+
   // If one component is NaN, all of them are, indicating a NaN time value.
   // [value]: the time value.
   DECL_ACCESSORS(value, Object)
@@ -7553,6 +7561,9 @@ class JSDate: public JSObject {
 
   DECLARE_CAST(JSDate)
 
+  // Returns the time value (UTC) identifying the current time.
+  static double CurrentTimeValue(Isolate* isolate);
+
   // Returns the date field with the specified index.
   // See FieldIndex for the list of date fields.
   static Object* GetField(Object* date, Smi* index);