Add histograms for deletion of session cookies on startup.

content/browser/net/sqlite_persistent_cookie_store.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 "content/browser/net/sqlite_persistent_cookie_store.h"
 
 #include <list>
 #include <map>
 #include <set>
 #include <utility>
@@ skipping 683 matching lines @@
       50);
 
   UMA_HISTOGRAM_CUSTOM_TIMES(
       "Cookie.TimeInitializeDomainMap",
       base::Time::Now() - start,
       base::TimeDelta::FromMilliseconds(1), base::TimeDelta::FromMinutes(1),
       50);
 
   initialized_ = true;
 
-  if (!restore_old_session_cookies_)
+  if (!restore_old_session_cookies_) {
+    base::Time start_time = base::Time::Now();
     DeleteSessionCookiesOnStartup();
+
+    UMA_HISTOGRAM_TIMES("Cookie.Startup.TimeSpentDeletingCookies",
+                        base::Time::Now() - start_time);
+    UMA_HISTOGRAM_COUNTS("Cookie.Startup.NumberOfCookiesDeleted",
+                         db_->GetLastChangeCount());

[erikwright (departed), 2015/05/12 19:39:50]

Either:

(1) Have DeleteSessionCookiesOnStartup return this count
(2) Put the metric reporting inside DeleteSessionCookiesOnStartup
(3) Inline the contents of DeleteSessionCookiesOnStartup here

Reason: It's not obvious from what we see here that
DeleteSessionCookiesOnStartup only executes a single statement. But this code
assumes that. If DeleteSessionCookiesOnStartup were later changed to (for
example) delete on a domain-by-domain basis, the assumption would be broken.

[erikchen, 2015/05/12 20:33:49]

Oh yes, good point. This logic originally started in
DeleteSessionCookiesOnStartup(), but got moved around while I was adding
different metrics. Thanks!

+  }
+
   return true;
 }
 
 void SQLitePersistentCookieStore::Backend::ChainLoadCookies(
     const LoadedCallback& loaded_callback) {
   DCHECK(background_task_runner_->RunsTasksOnCurrentThread());
   IncrementTimeDelta increment(&cookie_load_duration_);
 
   bool load_success = true;
 
@@ skipping 734 matching lines @@
         (config.session_cookie_mode ==
          CookieStoreConfig::RESTORED_SESSION_COOKIES)) {
       cookie_monster->SetPersistSessionCookies(true);
     }
   }
 
   return cookie_monster;
 }
 
 }  // namespace content