Add UMA metric of time to start the first render process

components/startup_metric_utils/browser/startup_metric_utils.h

Index: components/startup_metric_utils/browser/startup_metric_utils.h
diff --git a/components/startup_metric_utils/browser/startup_metric_utils.h b/components/startup_metric_utils/browser/startup_metric_utils.h
index 2e6fd0d3108d662352cd40e69f7760a4dda8e76e..6066d716056e51f2558e8b2acf85d513bdef8909 100644
--- a/components/startup_metric_utils/browser/startup_metric_utils.h
+++ b/components/startup_metric_utils/browser/startup_metric_utils.h
@@ -83,8 +83,10 @@ void RecordRendererMainEntryTime(base::TimeTicks ticks);
 void RecordFirstWebContentsMainFrameLoad(base::TimeTicks ticks);
 
 // Call this with the time when the first web contents had a non-empty paint,
-// only if the first web contents was unimpended in its attempt to do so.
-void RecordFirstWebContentsNonEmptyPaint(base::TimeTicks ticks);
+// only if the first web contents was unimpeded in its attempt to do so.
+void RecordFirstWebContentsNonEmptyPaint(
+    base::TimeTicks now,
+    base::TimeTicks render_process_host_init_time);
 
 // Call this with the time when the first web contents began navigating its main
 // frame. Adds a suffix to its metrics according to |workload|.