Limit grantTrust() duration to DevicePolicy-imposed limit.

Fixes bug 17046034

Change-Id: I5c512c2d05e7e0ed81eaf0dcafacc6f62a5c5937
diff --git a/core/java/android/app/admin/DevicePolicyManager.java b/core/java/android/app/admin/DevicePolicyManager.java
index 41bbb87..a16cd7f 100644
--- a/core/java/android/app/admin/DevicePolicyManager.java
+++ b/core/java/android/app/admin/DevicePolicyManager.java
@@ -1374,7 +1374,7 @@
      * @param admin The name of the admin component to check, or null to aggregate
      * all admins.
      * @return time in milliseconds for the given admin or the minimum value (strictest) of
-     * all admins if admin is null.
+     * all admins if admin is null. Returns 0 if there are no restrictions.
      */
     public long getMaximumTimeToLock(ComponentName admin) {
         return getMaximumTimeToLock(admin, UserHandle.myUserId());