Add new metrics descriptions.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 3b58faabf4f253fd98bc20f55d0d22a595ac4cdf..112318db0dc75e9ce4532b87d3e83e8d09c00ea4 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -9193,6 +9193,69 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Platform.DiskUsage.1User" units="KB">
+  <summary>
+    Statistics on pass-through directory usage. Device has exactly 1 user.
+    Logged once a day, if free disk space is below 1GB.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.2Users" units="KB">
+  <summary>
+    Statistics on pass-through directory usage. Device has exactly 2 users.
+    Logged once a day, if free disk space is below 1GB.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.3Users" units="KB">
+  <summary>
+    Statistics on pass-through directory usage. Device has exactly 3 users.
+    Logged once a day, if free disk space is below 1GB.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.4Users" units="KB">
+  <summary>
+    Statistics on pass-through directory usage. Device has exactly 4 users.
+    Logged once a day, if free disk space is below 1GB.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.5Users" units="KB">
+  <summary>
+    Statistics on pass-through directory usage. Device has exactly 5 users.
+    Logged once a day, if free disk space is below 1GB.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.6Users" units="KB">
+  <summary>
+    Statistics on pass-through directory usage. Device has exactly 6 users.
+    Logged once a day, if free disk space is below 1GB.
+  </summary>
+</histogram>
+
+<histogram name="Platform.DiskUsage.7OrMoreUsers" units="KB">
+  <summary>
+    Statistics on pass-through directory usage. Device has at least 7 users.
+    Logged once a day, if free disk space is below 1GB.
+  </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>
@@ -21655,6 +21718,23 @@ other types of suffix sets.
   <affected-histogram name="Cros.ClickOnShelf"/>
 </fieldtrial>
 
+<fieldtrial name="DiskUsagePerDirectory" separator=".">
+  <group name="Cache_Avg"/>

[Alexei Svitkine (slow), 2013/07/24 18:55:17]

Please add a label="..." attribute explaining these.

+  <group name="Cache_Max"/>
+  <group name="Downloads_Avg"/>
+  <group name="Downloads_Max"/>
+  <group name="GCache_Avg"/>
+  <group name="GCache_Max"/>
+  <group name="Bookmark"/>
+  <affected-histogram name="Platform.DiskUsage.1User"/>

[Alexei Svitkine (slow), 2013/07/24 18:55:17]

I'm not sure if you already submitted the other CL, but if you have the
flexibility of changing these on the CrOS CL, it would be better to re-order the
parts of the name, so that 1User, 2Users, 3Users, etc are actual "group" entries
in this model (i.e. suffixes), so that you can have proper descriptions for
Cache vs. Downloads, etc.

Then, your histograms would look like:

Platform.DiskUsage.Cache_Max.2Users

[Denis Kuznetsov (DE-MUC), 2013/07/25 17:04:36]

Done.

+  <affected-histogram name="Platform.DiskUsage.2Users"/>
+  <affected-histogram name="Platform.DiskUsage.3Users"/>
+  <affected-histogram name="Platform.DiskUsage.4Users"/>
+  <affected-histogram name="Platform.DiskUsage.5Users"/>
+  <affected-histogram name="Platform.DiskUsage.6Users"/>
+  <affected-histogram name="Platform.DiskUsage.7OrMoreUsers"/>
+</fieldtrial>
+
 <fieldtrial name="DnsImpact2">
   <group name="disabled_prefetch"
       label="DNS pre-resolving is disabled in these clients"/>