Don't push histograms to browser after every page load when persistence is enabled.

chrome/renderer/page_load_histograms.cc

 // Copyright (c) 2012 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/renderer/page_load_histograms.h"
 
 #include <stddef.h>
 
 #include <memory>
 #include <string>
 
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
+#include "base/metrics/persistent_histogram_allocator.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/time/time.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/renderer/searchbox/search_bouncer.h"
 #include "components/data_reduction_proxy/content/common/data_reduction_proxy_messages.h"
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_params.h"
@@ skipping 843 matching lines @@
   DumpDeprecatedHistograms(frame->performance(), document_state,
                            data_reduction_proxy_was_used,
                            came_from_websearch,
                            websearch_chrome_joint_experiment_id,
                            is_preview,
                            scheme_type);
 
   // Log the PLT to the info log.
   LogPageLoadTime(document_state, frame->dataSource());
 
-  // Since there are currently no guarantees that renderer histograms will be
-  // sent to the browser, we initiate a PostTask here to be sure that we send
-  // the histograms we generated.  Without this call, pages that don't have an
-  // on-close-handler might generate data that is lost when the renderer is
-  // shutdown abruptly (perchance because the user closed the tab).
-  // TODO(jar) BUG=33233: This needs to be moved to a PostDelayedTask, and it
-  // should post when the onload is complete, so that it doesn't interfere with
-  // the next load.
-  content::RenderThread::Get()->UpdateHistograms(
-      content::kHistogramSynchronizerReservedSequenceNumber);
+  // If persistent histograms are not enabled, initiate a PostTask here to be
+  // sure that we send the histograms generated. Without this call, pages
+  // that don't have an on-close-handler might generate data that is lost if
+  // the renderer is shutdown abruptly (e.g. the user closed the tab).

[Alexei Svitkine (slow), 2016/08/10 15:44:28]

Maybe add a TODO to clean this up when persistent becomes the default?

[bcwhite, 2016/08/10 16:30:55]

Done.

+  if (!base::GlobalHistogramAllocator::Get()) {
+    content::RenderThread::Get()->UpdateHistograms(
+        content::kHistogramSynchronizerReservedSequenceNumber);
+  }
 }
 
 void PageLoadHistograms::FrameWillClose(WebFrame* frame) {
   Dump(frame);
 }
 
 void PageLoadHistograms::ClosePage() {
   // TODO(davemoore) This code should be removed once willClose() gets
   // called when a page is destroyed. page_load_histograms_.Dump() is safe
   // to call multiple times for the same frame, but it will simplify things.
@@ skipping 13 matching lines @@
   Time start = document_state->start_load_time();
   Time finish = document_state->finish_load_time();
   // TODO(mbelshe): should we log more stats?
   VLOG(1) << "PLT: " << (finish - start).InMilliseconds() << "ms "
           << url.spec();
 }
 
 void PageLoadHistograms::OnDestruct() {
   delete this;
 }