Add new metrics descriptions.

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 9175 matching lines @@
   </summary>
 </histogram>
 
 <histogram name="Platform.CrOSEvent" enum="CrosEventEnum">
   <summary>
     Generic event of interest from Chrome OS.  Intended mainly to help assess
     the frequency of rare error conditions.
   </summary>
 </histogram>
 
+<histogram name="Platform.DiskUsage.HighUserCount.Cache_Avg" units="KB">

[Alexei Svitkine (slow), 2013/07/23 19:49:04]

You can make these less verbose by using a fieldtrial construct in the XML file
to give all of these histograms a common prefix. See the example at the top of
histograms.xml.

[Denis Kuznetsov (DE-MUC), 2013/07/24 14:13:41]

I could not find ProfilePictureDownload using chrome code search, but I've used
the prefix.

+  <summary>
+    Average size of user's Cache directory. Device has more than 6 users. Logged
+    once a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.HighUserCount.Cache_Max" units="KB">
+  <summary>
+    Maximum size of user's Cache directory. Device has more than 6 users. Logged
+    once a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.HighUserCount.Downloads_Avg" units="KB">
+  <summary>
+    Average size of user's Cache directory. Device has more than 6 users. Logged
+    once a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.HighUserCount.Downloads_Max" units="KB">
+  <summary>
+    Maximum size of user's Cache directory. Device has more than 6 users. Logged
+    once a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.HighUserCount.GCache_Avg" units="KB">
+  <summary>
+    Average size of user's GCache directory. Device has more than 6 users.
+    Logged once a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.HighUserCount.GCache_Max" units="KB">
+  <summary>
+    Maximum size of user's GCache directory. Device has more than 6 users.
+    Logged once a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.LowUserCount.Cache_Avg" units="KB">
+  <summary>
+    Average size of user's Cache directory. Device has 1 to 3 users. Logged once
+    a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.LowUserCount.Cache_Max" units="KB">
+  <summary>
+    Maximum size of user's Cache directory. Device has 1 to 3 users. Logged once
+    a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.LowUserCount.Downloads_Avg" units="KB">
+  <summary>
+    Average size of user's Cache directory. Device has 1 to 3 users. Logged once
+    a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.LowUserCount.Downloads_Max" units="KB">
+  <summary>
+    Maximum size of user's Cache directory. Device has 1 to 3 users. Logged once
+    a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.LowUserCount.GCache_Avg" units="KB">
+  <summary>
+    Average size of user's GCache directory. Device has 1 to 3 users. Logged
+    once a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.LowUserCount.GCache_Max" units="KB">
+  <summary>
+    Maximum size of user's GCache directory. Device has 1 to 3 users. Logged
+    once a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.MediumUserCount.Cache_Avg" units="KB">
+  <summary>
+    Average size of user's Cache directory. Device has 4 to 6 users. Logged once
+    a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.MediumUserCount.Cache_Max" units="KB">
+  <summary>
+    Maximum size of user's Cache directory. Device has 4 to 6 users. Logged once
+    a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.MediumUserCount.Downloads_Avg" units="KB">
+  <summary>
+    Average size of user's Cache directory. Device has 4 to 6 users. Logged once
+    a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.MediumUserCount.Downloads_Max" units="KB">
+  <summary>
+    Maximum size of user's Cache directory. Device has 4 to 6 users. Logged once
+    a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.MediumUserCount.GCache_Avg" units="KB">
+  <summary>
+    Average size of user's GCache directory. Device has 4 to 6 users. Logged
+    once a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.MediumUserCount.GCache_Max" units="KB">
+  <summary>
+    Maximum size of user's GCache directory. Device has 4 to 6 users. Logged
+    once a day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.OldestUserOnDevice">
+  <summary>
+    Days since last login of the least recently user on device. Logged once a
+    day, if disk usage is high.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.UsersOnDevice">
+  <summary>
+    Number of user home dirs on device. Logged once a day, if disk usage is
+    high.
+  </summary>
+</histogram>
+
 <histogram name="Platform.DiskUsageCache" units="KB">
   <summary>KB in use in the /cache filesystem tree. Logged once a day.</summary>
 </histogram>
 
 <histogram name="Platform.DiskUsageChronos" units="KB">
   <summary>
     Chrome OS KB in use in the /home/chronos filesystem tree. Logged once a day
     during log file cleanup.
   </summary>
 </histogram>
@@ skipping 14242 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>