Add UMA metric of time to start the first render process

components/startup_metric_utils/browser/startup_metric_utils.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_STARTUP_METRIC_UTILS_BROWSER_STARTUP_METRIC_UTILS_H_
 #define COMPONENTS_STARTUP_METRIC_UTILS_BROWSER_STARTUP_METRIC_UTILS_H_
 
 #include "base/time/time.h"
 
 class PrefRegistrySimple;
@@ skipping 65 matching lines @@
 // call to this function is used to compute
 // Startup.LoadTime.BrowserMainToRendererMain. Further calls to this
 // function are ignored.
 void RecordRendererMainEntryTime(base::TimeTicks ticks);
 
 // Call this with the time when the first web contents loaded its main frame,
 // only if the first web contents was unimpended in its attempt to do so.
 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.

[tdresser, 2017/05/29 13:38:02]

Can we fix unimpended -> unimpeded while we're here?

[hans, 2017/05/31 19:48:57]

Done.

-void RecordFirstWebContentsNonEmptyPaint(base::TimeTicks ticks);
+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|.
 void RecordFirstWebContentsMainNavigationStart(base::TimeTicks ticks,
                                                WebContentsWorkload workload);
 
 // Call this with the time when the first web contents successfully committed
 // its navigation for the main frame.
 void RecordFirstWebContentsMainNavigationFinished(base::TimeTicks ticks);
 
 // Call this with the time when the Browser window painted its children for the
 // first time.
 void RecordBrowserWindowFirstPaint(base::TimeTicks ticks);
 
 // Call this with the time when the Browser window painted its children for the
 // first time and we got a CompositingEnded after that.
 void RecordBrowserWindowFirstPaintCompositingEnded(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.
 base::TimeTicks MainEntryPointTicks();
 
 }  // namespace startup_metric_utils
 
 #endif  // COMPONENTS_STARTUP_METRIC_UTILS_BROWSER_STARTUP_METRIC_UTILS_H_