Add Platform.BatteryAbsent histogram to track "missing battery icon" bug

We'll add an upstart job on the Chrome OS side to log whether the failure
is seen on each boot.

BUG=458878
R=jrbarnette@chromium.org,vapier@chromium.org,semenzato@chromium.org,olofj@chromium.org,ejcaruso@chromium.org,isherman@chromium.org
Signed-off-by: Kevin Cernekee <cernekee@chromium.org>

Review URL: https://codereview.chromium.org/1133493008

Cr-Commit-Position: refs/heads/master@{#330863}

tools/metrics/histograms/histograms.xml

@@ -26961,6 +26961,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Platform.BatteryAbsent" enum="BooleanAbsent">
+  <owner>cernekee@chromium.org</owner>
+  <summary>
+    Indicates whether the kernel's ACPI Smart Battery System driver logged an
+    error trying to find the battery on boot.
+  </summary>
+</histogram>
+
 <histogram name="Platform.BootSectorsRead">
   <owner>sonnyrao@chromium.org</owner>
   <summary>
@@ -48324,6 +48332,11 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="1" label="True"/>
 </enum>
 
+<enum name="BooleanAbsent" type="int">
+  <int value="0" label="Not Absent"/>
+  <int value="1" label="Absent"/>
+</enum>
+
 <enum name="BooleanAccepted" type="int">
   <int value="0" label="Not Accepted"/>
   <int value="1" label="Accepted"/>