[turbofan] Infer proper type for calls to Date.now.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index c60bdebe5148a3dd5dba1fbcb71f53a02526da19..cbb8a78d0f5c0be0533e8c92a3e5c1e017d17513 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -7237,6 +7237,7 @@ class Script: public Struct {
   V(Array.prototype, push, ArrayPush)                       \
   V(Array.prototype, pop, ArrayPop)                         \
   V(Array.prototype, shift, ArrayShift)                     \
+  V(Date, now, DateNow)                                     \
   V(Date.prototype, getDate, DateGetDate)                   \
   V(Date.prototype, getDay, DateGetDay)                     \
   V(Date.prototype, getFullYear, DateGetFullYear)           \