Changing return value of request animation frame.

lib/html/templates/html/dart2js/impl_Window.darttemplate

Index: lib/html/templates/html/dart2js/impl_Window.darttemplate
diff --git a/lib/html/templates/html/dart2js/impl_Window.darttemplate b/lib/html/templates/html/dart2js/impl_Window.darttemplate
index e7e156add95e27cef4b4feb5d22c99ed070d0f38..6de6a1d3912957efc89983a6872c4bc896af8e85 100644
--- a/lib/html/templates/html/dart2js/impl_Window.darttemplate
+++ b/lib/html/templates/html/dart2js/impl_Window.darttemplate
@@ -107,7 +107,9 @@ class $CLASSNAME$EXTENDS$IMPLEMENTS native "@*DOMWindow" {
    }
    if (this.requestAnimationFrame && this.cancelAnimationFrame) return;
    this.requestAnimationFrame = function(callback) {
-       return window.setTimeout(callback, 16 /* 16ms ~= 60fps */);
+      return window.setTimeout(function() {
+        callback(Date.now());
+      }, 16 /* 16ms ~= 60fps */);
    };
    this.cancelAnimationFrame = function(id) { clearTimeout(id); }
 ''';