Substitute operation counting with a watchdog thread (477187, 2nd attempt, r=brendan/mrbkap/jst, sr=brendan/jst).

js/src/jsdate.cpp

@@ -2478,3 +2478,21 @@ js_DateGetMsecSinceEpoch(JSContext *cx, JSObject *obj)
         return 0;
     return utctime;
 }
+
+#ifdef JS_THREADSAFE
+#include "prinrval.h"
+
+uint32 
+js_IntervalNow() 
+{
+    return uint32(PR_IntervalToMilliseconds(PR_IntervalNow()));
+}
+
+#else /* !JS_THREADSAFE */
+
+uint32 
+js_IntervalNow() 
+{
+    return uint32(PRMJ_Now() / PRMJ_USEC_PER_MSEC);
+}
+#endif