net: Remove code for session cookie deletion experiment.

The original experiment attempted to measure the effect of deleting session
cookies at shutdown on startup time. This experiment was flawed, because there
are several cases where Chrome doesn't want to delete session cookies during
shutdown.

BUG=488314

Review URL: https://codereview.chromium.org/1333033002

Cr-Commit-Position: refs/heads/master@{#348252}

net/extras/sqlite/sqlite_persistent_cookie_store.cc

@@ -16,7 +16,6 @@
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/sequenced_task_runner.h"
@@ -45,15 +44,6 @@ namespace {
 // CPU or I/O with these low priority requests immediately after start up.
 const int kLoadDelayMilliseconds = 0;
 
-const char kDeleteAtShutdown[] = "DeleteAtShutdown";
-const char kSessionCookieDeletionStrategy[] = "SessionCookieDeletionStrategy";
-
-bool ShouldDeleteSessionCookiesAtShutdown() {
-  const std::string group_name =
-      base::FieldTrialList::FindFullName(kSessionCookieDeletionStrategy);
-  return group_name == kDeleteAtShutdown;
-}
-
 }  // namespace
 
 namespace net {
@@ -89,9 +79,7 @@ class SQLitePersistentCookieStore::Backend
       const scoped_refptr<base::SequencedTaskRunner>& background_task_runner,
       bool restore_old_session_cookies,
       CookieCryptoDelegate* crypto_delegate)
-      : delete_session_cookies_at_shutdown_(
-            ShouldDeleteSessionCookiesAtShutdown()),
-        path_(path),
+      : path_(path),
         num_pending_(0),
         initialized_(false),
         corruption_detected_(false),
@@ -226,8 +214,6 @@ class SQLitePersistentCookieStore::Backend
 
   void DeleteSessionCookiesOnStartup();
 
-  void DeleteSessionCookiesOnShutdown();
-
   void BackgroundDeleteAllInList(const std::list<CookieOrigin>& cookies);
 
   void DatabaseErrorCallback(int error, sql::Statement* stmt);
@@ -243,7 +229,6 @@ class SQLitePersistentCookieStore::Backend
   void FinishedLoadingCookies(const LoadedCallback& loaded_callback,
                               bool success);
 
-  bool delete_session_cookies_at_shutdown_;
   const base::FilePath path_;
   scoped_ptr<sql::Connection> db_;
   sql::MetaTable meta_table_;
@@ -1193,10 +1178,6 @@ void SQLitePersistentCookieStore::Backend::Close(
 void SQLitePersistentCookieStore::Backend::InternalBackgroundClose(
     const base::Closure& callback) {
   DCHECK(background_task_runner_->RunsTasksOnCurrentThread());
-
-  if (delete_session_cookies_at_shutdown_)
-    DeleteSessionCookiesOnShutdown();
-
   // Commit any pending operations
   Commit();
 
@@ -1271,22 +1252,6 @@ void SQLitePersistentCookieStore::Backend::DeleteSessionCookiesOnStartup() {
                        db_->GetLastChangeCount());
 }
 
-void SQLitePersistentCookieStore::Backend::DeleteSessionCookiesOnShutdown() {
-  DCHECK(background_task_runner_->RunsTasksOnCurrentThread());
-
-  if (!db_)
-    return;
-
-  base::Time start_time = base::Time::Now();
-  if (!db_->Execute("DELETE FROM cookies WHERE persistent != 1"))
-    LOG(WARNING) << "Unable to delete session cookies.";
-
-  UMA_HISTOGRAM_TIMES("Cookie.Shutdown.TimeSpentDeletingCookies",
-                      base::Time::Now() - start_time);
-  UMA_HISTOGRAM_COUNTS("Cookie.Shutdown.NumberOfCookiesDeleted",
-                       db_->GetLastChangeCount());
-}
-
 void SQLitePersistentCookieStore::Backend::BackgroundDeleteAllInList(
     const std::list<CookieOrigin>& cookies) {
   DCHECK(background_task_runner_->RunsTasksOnCurrentThread());

tools/metrics/histograms/histograms.xml

@@ -4968,6 +4968,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="Cookie.Shutdown.NumberOfCookiesDeleted">
+  <obsolete>
+    Deprecated as of 9/2015. The associated experiment was flawed.
+  </obsolete>
   <owner>erikchen@chromium.org</owner>
   <summary>
     The number of session cookies deleted on shutdown. This metric is emitted
@@ -4976,6 +4979,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="Cookie.Shutdown.TimeSpentDeletingCookies" units="ms">
+  <obsolete>
+    Deprecated as of 9/2015. The associated experiment was flawed.
+  </obsolete>
   <owner>erikchen@chromium.org</owner>
   <summary>
     The amount of time required to delete session cookies on shutdown. This