Battery Status API: add UMA logging for Linux.

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 5f84acab589b5a01833a077269d67b967a632eef..36f8ed63d3de28d1e7ed30e4fc1e8644bfc995b0 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -1927,6 +1927,16 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="BatteryStatus.NumberBatteriesLinux">
+  <owner>timvolodine@chromium.org</owner>
+  <summary>
+    Number of batteries reported by the UPower service on Linux at the start of
+    the Battery Status API. Note that the histogram is capped at max value 5, so
+    that any number larger than the max value will be counted in the last bucket
+    (corresponding to the value 5).

[Ilya Sherman, 2014/08/21 17:29:56]

nit: You could associate an <enum> with this histogram, and label the overflow
bucket as "5+".

+  </summary>
+</histogram>
+
 <histogram name="BatteryStatus.StartAndroid" enum="BooleanSuccess">
   <owner>timvolodine@chromium.org</owner>
   <summary>