Add metrics for interactions with the Apps Launcher promo dialog.

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 160 matching lines @@
   </summary>
 </histogram>
 
 <histogram name="Apps.AppLaunch" enum="AppLaunch">
   <summary>
     The number of times v2 packaged apps are launched grouped by
     extension_misc::AppLaunchBuckets. See also Extensions.AppLaunch.
   </summary>
 </histogram>
 
+<histogram name="Apps.AppLauncherPromo" enum="AppLauncherPromo">
+  <summary>Interactions with the App Launcher promo dialog.</summary>
+</histogram>
+
 <histogram name="AsyncDNS.ConfigChange" enum="BooleanSuccess">
   <summary>
     Whether DnsConfigService::OnConfigChange actually corresponded to a change
     in DnsConfig.
   </summary>
 </histogram>
 
 <histogram name="AsyncDNS.ConfigNotifyInterval" units="milliseconds">
   <summary>
     Duration of time between calls to DnsConfigService::InvalidateConfig.
@@ skipping 12140 matching lines @@
   <int value="21" label="APP_LIST_SEARCH"/>
 </enum>
 
 <enum name="AppLaunchContainer" type="int">
   <int value="0" label="LAUNCH_WINDOW"/>
   <int value="1" label="LAUNCH_PANEL"/>
   <int value="2" label="LAUNCH_TAB"/>
   <int value="3" label="LAUNCH_NONE (v2 packaged apps)"/>
 </enum>
 
+<enum name="AppLauncherPromo" type="int">
+  <int value="0" label="Already installed"/>
+  <int value="1" label="Shown"/>
+  <int value="2" label="Dismissed"/>
+  <int value="3" label="Learn more"/>
+</enum>
+
 <enum name="AppPromoAction" type="int">
   <int value="0" label="PROMO_LAUNCH_APP"/>
   <int value="1" label="PROMO_LAUNCH_WEB_STORE"/>
   <int value="2" label="PROMO_CLOSE"/>
   <int value="3" label="PROMO_EXPIRE"/>
   <int value="4" label="PROMO_SEEN"/>
 </enum>
 
 <enum name="AppsPageDragSource" type="int">
   <int value="0" label="Same apps pane"/>
@@ skipping 7744 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>