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

chrome/browser/chromeos/policy/device_cloud_policy_store_chromeos.h

Index: chrome/browser/chromeos/policy/device_cloud_policy_store_chromeos.h
diff --git a/chrome/browser/chromeos/policy/device_cloud_policy_store_chromeos.h b/chrome/browser/chromeos/policy/device_cloud_policy_store_chromeos.h
index cb9c78ab97b0b69cfeeda6f34acbf7686d9094d0..39e0269357c64bd6368bc76b42cb2c7cdec91c55 100644
--- a/chrome/browser/chromeos/policy/device_cloud_policy_store_chromeos.h
+++ b/chrome/browser/chromeos/policy/device_cloud_policy_store_chromeos.h
@@ -76,6 +76,9 @@ class DeviceCloudPolicyStoreChromeOS
 
   scoped_refptr<base::SequencedTaskRunner> background_task_runner_;
 
+  // Ensure that UMA stats are only reported once per session.

[Mattias Nissler (ping if slow), 2014/05/26 07:54:11]

This is not per session, but per Chrome restart. And you definitively will see
distortion due to different usage patterns the way you have it now. Other code
makes decisions based on time, i.e. reporting only if we haven't for the last 24
hours - maybe that's more appropriate here?

[Thiemo Nagel, 2014/05/26 10:53:55]

I'd like to keep it as simple as possible, thus I've updated the description
instead of adding a once-in-24-hours logic.

+  bool uma_done_;
+
   base::WeakPtrFactory<DeviceCloudPolicyStoreChromeOS> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DeviceCloudPolicyStoreChromeOS);