Add UMA for policy load result of enrolled Chrome OS devices.

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 4acd7674c4777fd6ac52a8ad8c407efa76b06fd4..5591b01d66f1fba2b15c57feb2bae56220f2dc17 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -4937,6 +4937,15 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Enterprise.EnrolledPolicyLoad" enum="EnterpriseDeviceSettingsServiceStatusType">
+  <owner>tnagel@chromium.org</owner>
+  <summary>
+    Status of loading device policy on an enterprise-enrolled (checked against
+    install_attributes.pb) Chrome OS device.  Filled once during session
+    startup, after first successful device policy read.
+  </summary>
+</histogram>
+
 <histogram name="Enterprise.ONC.PolicyValidation" enum="BooleanSuccess">
   <owner>joaodasilva@chromium.org</owner>
   <summary>Result of the OpenNetworkConfiguration policy validation.</summary>
@@ -33315,6 +33324,17 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="902" label="SERVICE_POLICY_NOT_FOUND"/>
 </enum>
 
+<enum name="EnterpriseDeviceSettingsServiceStatusType" type="int">
+  <int value="0" label="Success"/>
+  <int value="1" label="Key unavailable"/>
+  <int value="2" label="Policy error"/>
+  <int value="3" label="Operation failed"/>
+  <int value="4" label="No policy"/>
+  <int value="5" label="Invalid policy"/>
+  <int value="6" label="Validation error"/>
+  <int value="7" label="Success but has no DM token"/>
+</enum>
+
 <enum name="EnterpriseDMTokenType" type="int">
   <summary>
     Result of DMToken operations as defined in