Update Timing2 to PaintTiming in comments.

tools/metrics/rappor/rappor.xml

 <!--
 Copyright 2015 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.
 -->
 
 <rappor-configuration>
 <!--
 This file is used to generate a comprehensive list of Chrome rappor metrics
 along with a detailed description for each histogram. See the design doc at
@@ skipping 999 matching lines @@
 </rappor-metric>
 
 <rappor-metric name="PageLoad.CoarseTiming.NavigationToFirstContentfulPaint"
     type="UMA_RAPPOR_TYPE">
   <owner>csharrison@chromium.org</owner>
   <owner>bmcquade@chromium.org</owner>
   <summary>
     The eTLD+1 of the website visited, along with a bitfield representing
     bucket membership in a coarse histogram of time from navigation start to the
     time the first real content (text/image) is painted on the screen (See
-    PageLoad.Timing2.NavigationToFirstContentfulPaint). The bucket's name is the
-    histogram's lower bound. Tracks the same sites that the rest of the
+    PageLoad.PaintTiming.NavigationToFirstContentfulPaint). The bucket's name is
+    the histogram's lower bound. Tracks the same sites that the rest of the
     PageLoad.* histogram metrics track, i.e. http/s, html, main frame
     navigations. Metrics are only recorded for navigations that reached first
     contentful paint entirely in the foreground.
   </summary>
   <string-field name="Domain">
     <summary>
       The domain+registry of the URL.
     </summary>
   </string-field>
   <flags-field name="Bucket">
@@ skipping 849 matching lines @@
     <flag>Bit 1: IS_REPEAT_VISIT</flag>
     <summary>
       Bitfield of the state from an SSL warning interstitial.
     </summary>
   </flags-field>
 </rappor-metric>
 
 </rappor-metrics>
 
 </rappor-configuration>