UsageStats: Use new settings key idle_duration2 for app idle

Ignores the old, re-appropriated key "idle_duration" which is now
set to a high value in order to force disable app idle on devices
with bug b/26355386

Bug:26355386
Change-Id: Iff9de843ad6e547d29c1583687fc7f7ce7e15090
diff --git a/core/java/android/provider/Settings.java b/core/java/android/provider/Settings.java
index 9a7d7bb..87922b0 100644
--- a/core/java/android/provider/Settings.java
+++ b/core/java/android/provider/Settings.java
@@ -7281,10 +7281,12 @@
          * The following keys are supported:
          *
          * <pre>
-         * idle_duration        (long)
+         * idle_duration2       (long)
          * wallclock_threshold  (long)
          * parole_interval      (long)
          * parole_duration      (long)
+         *
+         * idle_duration        (long) // This is deprecated and used to circumvent b/26355386.
          * </pre>
          *
          * <p>