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

src/date.h

Index: src/date.h
diff --git a/src/date.h b/src/date.h
index 035ead6d48453aa0eecf35f90f5541e0144f86b8..41df2f42e88ebb175ba9da4dd7dbd0258a870e87 100644
--- a/src/date.h
+++ b/src/date.h
@@ -190,6 +190,10 @@ class DateCache {
   // the first day of the given month in the given year.
   int DaysFromYearMonth(int year, int month);
 
+  // Breaks down the time value.
+  void BreakDown(int64_t time_ms, int* year, int* month, int* day, int* weekday,

[Camillo Bruni, 2016/01/05 10:26:59]

BreakDownTime might be a bit more obivous.

[Benedikt Meurer, 2016/01/05 10:30:59]

Done.

+                 int* hour, int* min, int* sec, int* ms);
+
   // Cache stamp is used for invalidating caches in JSDate.
   // We increment the stamp each time when the timezone information changes.
   // JSDate objects perform stamp check and invalidate their caches if