chromeos: Add descriptions for power manager metrics.

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 6260 matching lines @@
 <histogram name="Plugin.PpapiBrokerLoadResult" enum="PluginLoadResult">
   <summary>The result from an attempt to load a PPAPI broker.</summary>
 </histogram>
 
 <histogram name="Plugin.PpapiPluginLoadResult" enum="PluginLoadResult">
   <summary>The result from an attempt to load a PPAPI plugin.</summary>
 </histogram>
 
 <histogram name="Power.BacklightLevelOnAC" units="%">
   <summary>
-    The level of the backlight as a percentage when the user is on AC.
+    The level of the backlight as a percentage when the user is on AC. Sampled
+    periodically.

[Alexei Svitkine (slow), 2013/05/24 14:48:47]

Nit: Mention how frequently. Here and in the other ones.

[Daniel Erat, 2013/05/24 15:00:23]

Sure (although I'm concerned about the likelihood of something like this getting
out-of-date).

   </summary>
 </histogram>
 
 <histogram name="Power.BacklightLevelOnBattery" units="%">
   <summary>
     The level of the backlight as a percentage when the user is on battery.
+    Sampled periodically.
   </summary>
 </histogram>
 
 <histogram name="Power.BatteryChargeHealth" units="%">
   <summary>
     Chrome OS battery charge health percentage.  Sampled once when device starts
     charging.
   </summary>
 </histogram>
 
-<histogram name="Power.BatteryDischargeRate">
+<histogram name="Power.BatteryDischargeRate" units="mW">
   <summary>
     Chrome OS battery discharge rate in mW sampled when the device runs on
     battery.
   </summary>
 </histogram>
 
+<histogram name="Power.BatteryDischargeRateWhileSuspended" units="mW">
+  <summary>
+    Chrome OS battery discharge rate in mW while the system was suspended,
+    sampled at resume.  Only reported if the system was on battery power both
+    before suspending and after resuming and if the energy level didn't increase
+    while suspended (which would indicate that an AC adapter was connected).
+  </summary>
+</histogram>
+
 <histogram name="Power.BatteryInfoSample" enum="BatteryInfoSampleResult">
   <summary>
     Counts the number of times we have read the battery status from sysfs and if
     it gave us sensible values.
   </summary>
 </histogram>
 
 <histogram name="Power.BatteryRemainingAtEndOfSessionOnAC" units="%">
   <summary>
     Chrome OS remaining battery charge as percent of the maximum battery charge,
@@ skipping 158 matching lines @@
   </summary>
 </histogram>
 
 <histogram name="Power.KernelSuspendTimeOnBattery" units="milliseconds">
   <summary>
     The time that the kernel took to suspend-to-RAM the Chrome OS device when
     running on battery.
   </summary>
 </histogram>
 
+<histogram name="Power.KeyboardBacklightLevel" units="%">
+  <summary>
+    The level of the keyboard backlight as a percentage. Sampled periodically.
+  </summary>
+</histogram>
+
+<histogram name="Power.KeyboardBrightnessAdjust" enum="PowerBrightnessAdjust">
+  <summary>
+    Number of times the user has adjusted keyboard backlight brightness up and
+    down.
+  </summary>
+</histogram>
+
 <histogram name="Power.LengthOfSession" units="seconds">
   <summary>
     The length of time, in seconds, that a user spent in a single session.
     Values for this metric are clamped to 12 hours, so the last bucket should be
     considered to be including all metrics above 12 hours.
   </summary>
 </histogram>
 
 <histogram name="Power.MilliConsumptionPerHourIosOnActive">
   <summary>
@@ skipping 8823 matching lines @@
 <fieldtrial name="SSLResumption">
   <group name="Resume_Handshake" label="Session Resumption"/>
   <group name="Full_Handshake" label="Full"/>
   <affected-histogram name="Net.SSL_Connection_Latency"/>
   <affected-histogram name="Net.SSL_Connection_Latency_Google"/>
 </fieldtrial>
 
 </fieldtrials>
 
 </histogram-configuration>