Experiment to disable Prerendering with fast wind-down

chrome/browser/prerender/prerender_manager.cc

Index: chrome/browser/prerender/prerender_manager.cc
diff --git a/chrome/browser/prerender/prerender_manager.cc b/chrome/browser/prerender/prerender_manager.cc
index f97d9cef68fe32ccad83161c5424530b0f6eaf48..48a3c20c132b4aa3ba834929126ca6caa61738ab 100644
--- a/chrome/browser/prerender/prerender_manager.cc
+++ b/chrome/browser/prerender/prerender_manager.cc
@@ -18,6 +18,7 @@
 #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"
@@ -611,6 +612,30 @@ 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 {
@@ -882,6 +907,9 @@ std::unique_ptr<PrerenderHandle> PrerenderManager::AddPrerender(
     origin = ORIGIN_GWS_PRERENDER;
   }
 
+  if (origin != ORIGIN_OFFLINE && IsPrerenderSilenceExperiment())
+    return nullptr;
+
   GURL url = url_arg;
   GURL alias_url;
   if (IsControlGroup() && MaybeGetQueryStringBasedAliasURL(url, &alias_url))