Battery Status API: add UMA logging for Mac.

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 57cf2870374239a36267d9e56c954da44c72c716..d5ab3709b501966c427f1f061f063dab2a48a7a2 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -1937,7 +1937,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
 </histogram>
 
 <histogram name="BatteryStatus.NumberBatteriesLinux"
-    enum="BatteryStatusNumberBatteriesLinux">
+    enum="BatteryStatusNumberBatteries">
   <owner>timvolodine@chromium.org</owner>
   <summary>
     Number of batteries reported by the UPower service on Linux at the start of
@@ -1945,6 +1945,15 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="BatteryStatus.NumberBatteriesMac"
+    enum="BatteryStatusNumberBatteries">
+  <owner>timvolodine@chromium.org</owner>
+  <summary>
+    Number of batteries reported by MacOS at the start of the Battery Status
+    API.
+  </summary>
+</histogram>

[Ilya Sherman, 2014/09/04 23:02:48]

Why is this a separate histogram by platform, rather than having each platform
emit to a shared histogram?

[timvolodine, 2014/09/05 11:44:42]

the reason is that different platforms provide different information, e.g. afaik
on android there is no way to know how many batteries are in the system. Also we
want a breakdown by platform to see where we need to provide multi-battery
support, e.g. there is a suspicion that for mac the number of devices with
multiple batteries will be zero (or close to zero).

+
 <histogram name="BatteryStatus.StartAndroid" enum="BooleanSuccess">
   <owner>timvolodine@chromium.org</owner>
   <summary>
@@ -38079,7 +38088,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="2" label="Bad"/>
 </enum>
 
-<enum name="BatteryStatusNumberBatteriesLinux" type="int">
+<enum name="BatteryStatusNumberBatteries" type="int">
   <int value="5" label="5+"/>
 </enum>