Experiment to disable Prerendering with fast wind-down

chrome/browser/prerender/prerender_manager.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/browser/prerender/prerender_manager.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <functional>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/single_thread_task_runner.h"
 #include "base/sys_info.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
 #include "base/timer/elapsed_timer.h"
 #include "base/values.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/net/prediction_options.h"
 #include "chrome/browser/prerender/prerender_contents.h"
@@ skipping 573 matching lines @@
 // static
 bool PrerenderManager::IsNoUseGroup() {
   return GetMode() == PRERENDER_MODE_EXPERIMENT_NO_USE_GROUP;
 }
 
 // static
 bool PrerenderManager::IsNoStatePrefetch() {
   return GetMode() == PRERENDER_MODE_NOSTATE_PREFETCH;
 }
 
+bool PrerenderManager::IsPrerenderSilenceExperiment() {
+  // The group name should contain expiration time formatted as:
+  //   "ExperimentYes_expires_YYYY-MM-DDTHH:MM:SSZ".
+  std::string group_name =
+      base::FieldTrialList::FindFullName("PrerenderSilence");
+  const char kExperimentPrefix[] = "ExperimentYes";
+  if (!base::StartsWith(group_name, kExperimentPrefix,
+                        base::CompareCase::INSENSITIVE_ASCII)) {
+    return false;
+  }
+  const char kExperimentPrefixWithExpiration[] = "ExperimentYes_expires_";
+  if (!base::StartsWith(group_name, kExperimentPrefixWithExpiration,
+                        base::CompareCase::INSENSITIVE_ASCII)) {
+    return true;

[mattcary, 2016/08/25 13:51:18]

Do we really want a malformed experiment option to fail with prerender off? I
can't imagine how we'd get a badly formed flag except through some kind of
corruption, and so feel like we should return false in this case.

[droger, 2016/08/25 13:56:24]

Probably same for line 634 below.

[pasko, 2016/08/25 14:55:18]

I wanted a mere "ExperimentYes" (without a date) to enable the experiment,
sticky to the session. It might be that we'd want to try it on Beta?

On 2016/08/25 13:56:24, droger wrote:
Yeah, that one indeed is a malformed experiment, should disable.

I added a few comments for clarity, PTAL.

+  }
+  base::Time expiration_time;
+  if (!base::Time::FromString(
+          group_name.c_str() + (arraysize(kExperimentPrefixWithExpiration) - 1),
+          &expiration_time)) {
+    return true;
+  }
+  return GetCurrentTime() < expiration_time;
+}
+
 bool PrerenderManager::IsWebContentsPrerendering(
     const WebContents* web_contents,
     Origin* origin) const {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   PrerenderContents* prerender_contents = GetPrerenderContents(web_contents);
   if (!prerender_contents)
     return false;
 
   if (origin)
     *origin = prerender_contents->origin();
@@ skipping 251 matching lines @@
   // those prerenders is managed by the offliner.
   if (IsLowEndDevice() && origin != ORIGIN_OFFLINE)
     return nullptr;
 
   if ((origin == ORIGIN_LINK_REL_PRERENDER_CROSSDOMAIN ||
        origin == ORIGIN_LINK_REL_PRERENDER_SAMEDOMAIN) &&
       IsGoogleSearchResultURL(referrer.url)) {
     origin = ORIGIN_GWS_PRERENDER;
   }
 
+  if (origin != ORIGIN_OFFLINE && IsPrerenderSilenceExperiment())
+    return nullptr;
+
   GURL url = url_arg;
   GURL alias_url;
   if (IsControlGroup() && MaybeGetQueryStringBasedAliasURL(url, &alias_url))
     url = alias_url;
 
   // From here on, we will record a FinalStatus so we need to register with the
   // histogram tracking.
   histograms_->RecordPrerender(origin, url_arg);
 
   if (profile_->GetPrefs()->GetBoolean(prefs::kBlockThirdPartyCookies) &&
@@ skipping 412 matching lines @@
   DCHECK_EQ(1u, erased);
 }
 
 void PrerenderManager::SetPrerenderContentsFactoryForTest(
     PrerenderContents::Factory* prerender_contents_factory) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   prerender_contents_factory_.reset(prerender_contents_factory);
 }
 
 }  // namespace prerender