Add Startup.BrowserView.FirstPaint / .CompositingEnded histograms.

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 5ebb8ff5e77c397d7aeb649c001260765e611f68..eb174d91806bada224c1dce922702b93137033f1 100644
--- a/components/startup_metric_utils/browser/startup_metric_utils.h
+++ b/components/startup_metric_utils/browser/startup_metric_utils.h
@@ -92,6 +92,14 @@ void RecordFirstWebContentsMainNavigationStart(const base::TimeTicks& ticks,
 // its navigation for the main frame.
 void RecordFirstWebContentsMainNavigationFinished(const base::TimeTicks& ticks);
 
+// Call this with the time when the BrowserView painted its children for the
+// first time.
+void RecordBrowserViewFirstPaint(const base::TimeTicks& ticks);
+
+// Call this with the time when the BrowserView painted its children for the
+// first time and we got a CompositingEnded after that.
+void RecordBrowserViewFirstPaintCompositingEnded(const base::TimeTicks& ticks);
+
 // Returns the TimeTicks corresponding to main entry as recorded by
 // RecordMainEntryPointTime. Returns a null TimeTicks if a value has not been
 // recorded yet. This method is expected to be called from the UI thread.