Make file_util::CreateDirectory return an error, not just a bool

tools/metrics/histograms/histograms.xml

 <!--
 Copyright 2013 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.
 -->
 
 <!--
 This file is used to generate a comprehensive list of Chrome histograms along
 with a detailed description for each histogram.
 
@@ skipping 17040 matching lines @@
   <group name="LockFile" label="ChromiumEnv::LockFile"/>
   <group name="NewRandomAccessFile" label="ChromiumEnv::NewRandomAccessFile"/>
   <group name="RenameFile" label="ChromiumEnv::RenameFile"/>
   <affected-histogram name="LevelDBEnv.IDB.IOError."/>
   <affected-histogram name="LevelDBEnv.IOError."/>
 </fieldtrial>
 
 <fieldtrial name="LevelDBEnvRetry" separator="">
   <group name="RenameFile" label="RenameFile"/>
   <group name="LockFile" label="LockFile"/>
+  <group name="CreateDir" label="CreateDir"/>
   <affected-histogram name="LevelDBEnv.IDB.RetryRecoveredFromErrorIn"/>
   <affected-histogram name="LevelDBEnv.IDB.TimeUntilSuccessFor"/>
   <affected-histogram name="LevelDBEnv.RetryRecoveredFromErrorIn"/>
   <affected-histogram name="LevelDBEnv.TimeUntilSuccessFor"/>
 </fieldtrial>
 
 <fieldtrial name="LevelDBEnvRetryTimes" separator="">
   <obsolete>
     Deprecated 2013-04 in favor of LevelDBEnvRetry.
   </obsolete>
@@ skipping 1114 matching lines @@
   <group name="Disabled" label="Neither extra webstore link is visible"/>
   <group name="FooterLink" label="Link in bottom right of footer"/>
   <group name="PlusIcon" label="Plus icon in apps page"/>
   <affected-histogram name="Extensions.AppLaunch"/>
   <affected-histogram name="NewTabPage.DefaultPageType"/>
 </fieldtrial>
 
 </fieldtrials>
 
 </histogram-configuration>