Add UMA metric of time to start the first render process

components/startup_metric_utils/browser/startup_metric_utils.cc

 // 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.
 
 #include "components/startup_metric_utils/browser/startup_metric_utils.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <string>
@@ skipping 700 matching lines @@
     return;
   is_first_call = false;
   if (!ShouldLogStartupHistogram())
     return;
 
   UMA_HISTOGRAM_AND_TRACE_WITH_TEMPERATURE_AND_SAME_VERSION_COUNT(
       UMA_HISTOGRAM_LONG_TIMES_100, "Startup.FirstWebContents.MainFrameLoad2",
       g_process_creation_ticks.Get(), ticks);
 }
 
-void RecordFirstWebContentsNonEmptyPaint(base::TimeTicks ticks) {
+void RecordFirstWebContentsNonEmptyPaint(
+    base::TimeTicks now,
+    base::TimeTicks render_process_host_init_time) {
   static bool is_first_call = true;
-  if (!is_first_call || ticks.is_null())
+  if (!is_first_call || now.is_null())
     return;
   is_first_call = false;
 
   // Log Startup.BrowserMainToRendererMain now that the first renderer main
   // entry time and the startup temperature are known.
   RecordRendererMainEntryHistogram();
 
   if (!ShouldLogStartupHistogram())
     return;
 
   base::StackSamplingProfiler::SetProcessMilestone(
       metrics::CallStackProfileMetricsProvider::FIRST_NONEMPTY_PAINT);
   UMA_HISTOGRAM_AND_TRACE_WITH_TEMPERATURE_AND_SAME_VERSION_COUNT(
       UMA_HISTOGRAM_LONG_TIMES_100, "Startup.FirstWebContents.NonEmptyPaint2",
-      g_process_creation_ticks.Get(), ticks);
+      g_process_creation_ticks.Get(), now);
   UMA_HISTOGRAM_WITH_TEMPERATURE(
       UMA_HISTOGRAM_LONG_TIMES_100,
       "Startup.BrowserMessageLoopStart.To.NonEmptyPaint2",
-      ticks - g_message_loop_start_ticks.Get());
+      now - g_message_loop_start_ticks.Get());
+
+  UMA_HISTOGRAM_WITH_TEMPERATURE(

[gab, 2017/06/01 14:56:45]

UMA_HISTOGRAM_AND_TRACE_WITH_TEMPERATURE

so it appears in startup trace events.

+      UMA_HISTOGRAM_LONG_TIMES_100,
+      "Startup.FirstWebContents.RenderProcessHostInit.ToNonEmptyPaint",
+      now - render_process_host_init_time);
 }
 
 void RecordFirstWebContentsMainNavigationStart(base::TimeTicks ticks,
                                                WebContentsWorkload workload) {
   static bool is_first_call = true;
   if (!is_first_call || ticks.is_null())
     return;
   is_first_call = false;
   if (!ShouldLogStartupHistogram())
     return;
@@ skipping 67 matching lines @@
       UMA_HISTOGRAM_LONG_TIMES_100,
       "Startup.BrowserWindow.FirstPaint.CompositingEnded",
       g_process_creation_ticks.Get(), ticks);
 }
 
 base::TimeTicks MainEntryPointTicks() {
   return g_browser_main_entry_point_ticks.Get();
 }
 
 }  // namespace startup_metric_utils