Rename DiagnosticEvent to GoogleNowEvent

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 17586 matching lines @@
   <int value="1" label="CANT_GET_PARENT_PATH"/>
   <int value="2" label="CANT_GET_UDT_PATH"/>
   <int value="3" label="NOT_A_DIRECTORY"/>
   <int value="4" label="CANT_CREATE_DIR"/>
   <int value="5" label="CANT_WRITE_TO_PATH"/>
   <int value="6" label="UNSET"/>
 </enum>
 
 <enum name="GoogleNowEvent" type="int">
   <summary>
-    Events in Google Now component extension. See var DiagnosticEvent.
+    Events in Google Now component extension. See GoogleNowEvent in
+    chrome/browser/resources/google_now/background.js.
   </summary>
   <int value="0" label="REQUEST_FOR_CARDS_TOTAL"/>
   <int value="1" label="REQUEST_FOR_CARDS_SUCCESS"/>
   <int value="2" label="CARDS_PARSE_SUCCESS"/>
   <int value="3" label="DISMISS_REQUEST_TOTAL"/>
   <int value="4" label="DISMISS_REQUEST_SUCCESS"/>
   <int value="5" label="LOCATION_REQUEST"/>
   <int value="6" label="LOCATION_UPDATE"/>
   <int value="7" label="EXTENSION_START"/>
   <int value="8" label="SHOW_WELCOME_TOAST"/>
@@ skipping 6120 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>