Add UMA metric of time to start the first render process

chrome/browser/metrics/first_web_contents_profiler.cc

 // Copyright 2014 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 "chrome/browser/metrics/first_web_contents_profiler.h"
 
 #include <string>
 
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_list.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
 #include "components/metrics/profiler/tracking_synchronizer.h"
 #include "components/metrics/proto/profiler_event.pb.h"
 #include "components/startup_metric_utils/browser/startup_metric_utils.h"
 #include "content/public/browser/navigation_handle.h"
+#include "content/public/browser/render_frame_host.h"
+#include "content/public/browser/render_process_host.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/common/browser_side_navigation_policy.h"
 
 namespace {
 
 class FirstWebContentsProfiler : public content::WebContentsObserver {
  public:
   FirstWebContentsProfiler(content::WebContents* web_contents,
                            startup_metric_utils::WebContentsWorkload workload);
@@ skipping 67 matching lines @@
 void FirstWebContentsProfiler::DidFirstVisuallyNonEmptyPaint() {
   if (collected_paint_metric_)
     return;
   if (startup_metric_utils::WasMainWindowStartupInterrupted()) {
     FinishedCollectingMetrics(FinishReason::ABANDON_BLOCKING_UI);
     return;
   }
 
   collected_paint_metric_ = true;
   startup_metric_utils::RecordFirstWebContentsNonEmptyPaint(
-      base::TimeTicks::Now());
+      base::TimeTicks::Now(), web_contents()
+                                  ->GetMainFrame()
+                                  ->GetProcess()
+                                  ->GetInitTimeForNavigationMetrics());

[Bryan McQuade, 2017/05/26 22:28:42]

I notice that the comment for GetInitTimeForNavigationMetrics includes:
// Note: Do not use! Will disappear after PlzNavitate is completed.

Is there some other timestamp source we could use instead?

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

I'm not familiar with PlzNagigate (looks like something added in 2014), and I
think this is the timestamp I want. As far as I can tell, this is the one place
where we capture the timestamp for starting the render process.

(The comment is a little misleading, we set the timestamp after we've created
the ChildProcessLauncher, but IIUC, the actual launching happens
asynchronously.)

 
   metrics::TrackingSynchronizer::OnProfilingPhaseCompleted(
       metrics::ProfilerEventProto::EVENT_FIRST_NONEMPTY_PAINT);
 
   if (IsFinishedCollectingMetrics())
     FinishedCollectingMetrics(FinishReason::DONE);
 }
 
 void FirstWebContentsProfiler::DocumentOnLoadCompletedInMainFrame() {
   if (collected_load_metric_)
@@ skipping 129 matching lines @@
   const bool single_tab = browser_list->size() == 1 && tab_strip->count() == 1;
 
   // FirstWebContentsProfiler owns itself and is also bound to
   // |web_contents|'s lifetime by observing WebContentsDestroyed().
   new FirstWebContentsProfiler(web_contents,
                                single_tab ? WebContentsWorkload::SINGLE_TAB
                                           : WebContentsWorkload::MULTI_TABS);
 }
 
 }  // namespace metrics