Fix negative inactiveTime on creating a new user

Initialize the beginIdleTime to 0 rather than current time.

Bug: 21699099
Change-Id: Ib94a9198c4e80aea5d9de68c5cf5d6f8cfc79e0a

services/usage/java/com/android/server/usage/IntervalStats.java

@@ -48,7 +48,7 @@ class IntervalStats {
             usageStats.mPackageName = getCachedStringRef(packageName);
             usageStats.mBeginTimeStamp = beginTime;
             usageStats.mEndTimeStamp = endTime;
-            usageStats.mBeginIdleTime = endTime;
+            usageStats.mBeginIdleTime = 0;
             packageStats.put(usageStats.mPackageName, usageStats);
         }
         return usageStats;