Port rendering_stats' implementation to javascript

perf_insights/perf_insights/timeline_based_measurement/rendering_frame.html

Index: perf_insights/perf_insights/timeline_based_measurement/rendering_frame.html
diff --git a/perf_insights/perf_insights/timeline_based_measurement/rendering_frame.html b/perf_insights/perf_insights/timeline_based_measurement/rendering_frame.html
index 94653929f6a6c2070fc0d320511a2e761be360ec..73a7e1a2be42ed0e8bdc8fdc326e7f701a28da90 100644
--- a/perf_insights/perf_insights/timeline_based_measurement/rendering_frame.html
+++ b/perf_insights/perf_insights/timeline_based_measurement/rendering_frame.html
@@ -83,8 +83,9 @@ tr.exportTo('pi.tbm', function() {
              event.title === BEGIN_MAIN_FRAME_EVENT)) {
           beginFrameId = event.args['begin_frame_id'];
           if (beginFrameId === undefined) {
-            throw new Error(
+            var err = new Error(
                 'Event is missing a beginFrameId.');
+            throw err;

[dsinclair, 2015/09/22 16:08:31]

No need to store err into a variable, just throw new Error.

           }
         }
         beginFrameEventsById[beginFrameId] =