chromeos: Add descriptions for power manager metrics.

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 bd799a0e4cf00236e444701fc3212cade57d85bb..3d7075bf03b1fb1d19468bf2338a0eefe5bc7a31 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -6313,13 +6313,15 @@ other types of suffix sets.
 
 <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
+    every 30 seconds.
   </summary>
 </histogram>
 
 <histogram name="Power.BacklightLevelOnBattery" units="%">
   <summary>
     The level of the backlight as a percentage when the user is on battery.
+    Sampled every 30 seconds.
   </summary>
 </histogram>
 
@@ -6330,10 +6332,20 @@ other types of suffix sets.
   </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.
+    Chrome OS battery discharge rate in mW sampled every 30 seconds while 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, if the energy level didn't increase
+    while suspended (which would indicate that an AC adapter was connected), and
+    if the system was suspended for at least a minute.
   </summary>
 </histogram>
 
@@ -6515,6 +6527,20 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Power.KeyboardBacklightLevel" units="%">
+  <summary>
+    The level of the keyboard backlight as a percentage. Sampled every 30
+    seconds.
+  </summary>
+</histogram>
+
+<histogram name="Power.KeyboardBrightnessAdjust" enum="PowerBrightnessAdjust">
+  <summary>
+    Number of times the user has adjusted keyboard backlight brightness up and

[jar (doing other things), 2013/05/24 17:09:03]

When is this sampled?  At shutdown???  Each time the the system sleeps?

[Daniel Erat, 2013/05/24 22:02:29]

As discussed over IM, I've removed this histogram -- Chrome already reports
these adjustments as user actions.

I'm also removing the Power.BacklightLevel* histograms in conjunction with a
power manager change to stop reporting them. Is it acceptable to remove the
descriptions for them in this change, or should the descriptions be retained
indefinitely (since they have previously been reported)?

+    down.
+  </summary>
+</histogram>
+
 <histogram name="Power.LengthOfSession" units="seconds">
   <summary>
     The length of time, in seconds, that a user spent in a single session.