Change PrefService.ReadError histogram to sample success case.

chrome/browser/prefs/chrome_pref_service_factory.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/prefs/chrome_pref_service_factory.h"
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
 #include "base/file_util.h"
 #include "base/files/file_path.h"
@@ skipping 21 matching lines @@
 #include "chrome/browser/policy/policy_types.h"
 #endif
 
 using content::BrowserContext;
 using content::BrowserThread;
 
 namespace {
 
 // Shows notifications which correspond to PersistentPrefStore's reading errors.
 void HandleReadError(PersistentPrefStore::PrefReadError error) {
+  // Sample the histogram also for the successful case in order to get a
+  // baseline on the success rate in addition to the error distribution.
+  UMA_HISTOGRAM_ENUMERATION("PrefService.ReadError", error,
+                            PersistentPrefStore::PREF_READ_ERROR_MAX_ENUM);
+
   if (error != PersistentPrefStore::PREF_READ_ERROR_NONE) {
 #if !defined(OS_CHROMEOS)
     // Failing to load prefs on startup is a bad thing(TM). See bug 38352 for
     // an example problem that this can cause.
     // Do some diagnosis and try to avoid losing data.
     int message_id = 0;
     if (error <= PersistentPrefStore::PREF_READ_ERROR_JSON_TYPE) {
       message_id = IDS_PREFERENCES_CORRUPT_ERROR;
     } else if (error != PersistentPrefStore::PREF_READ_ERROR_NO_FILE) {
       message_id = IDS_PREFERENCES_UNREADABLE_ERROR;
     }
 
     if (message_id) {
       BrowserThread::PostTask(BrowserThread::UI, FROM_HERE,
                               base::Bind(&ShowProfileErrorDialog, message_id));
     }
 #else
     // On ChromeOS error screen with message about broken local state
     // will be displayed.
 #endif
-    UMA_HISTOGRAM_ENUMERATION("PrefService.ReadError", error,
-                              PersistentPrefStore::PREF_READ_ERROR_MAX_ENUM);
   }
 }
 
 void PrepareBuilder(
     PrefServiceSyncableBuilder* builder,
     const base::FilePath& pref_filename,
     base::SequencedTaskRunner* pref_io_task_runner,
     policy::PolicyService* policy_service,
     const scoped_refptr<PrefStore>& extension_prefs,
     bool async) {
@@ skipping 63 matching lines @@
   PrepareBuilder(&builder,
                  pref_filename,
                  pref_io_task_runner,
                  policy_service,
                  extension_prefs,
                  async);
   return builder.CreateSyncable(pref_registry.get());
 }
 
 }  // namespace chrome_prefs