Make the Context service constant for UsageStats public

This was an oversight in L, where we did not make this
service constant public.

Change-Id: I42e38cb5ef8420cadc1a4a6705821189d911ccfe
diff --git a/api/current.txt b/api/current.txt
index 7508a8d..27b107a 100644
--- a/api/current.txt
+++ b/api/current.txt
@@ -7277,6 +7277,7 @@
     field public static final java.lang.String TEXT_SERVICES_MANAGER_SERVICE = "textservices";
     field public static final java.lang.String TV_INPUT_SERVICE = "tv_input";
     field public static final java.lang.String UI_MODE_SERVICE = "uimode";
+    field public static final java.lang.String USAGE_STATS_SERVICE = "usagestats";
     field public static final java.lang.String USB_SERVICE = "usb";
     field public static final java.lang.String USER_SERVICE = "user";
     field public static final java.lang.String VIBRATOR_SERVICE = "vibrator";
diff --git a/core/java/android/content/Context.java b/core/java/android/content/Context.java
index 0daa8e2..e6bb09f 100644
--- a/core/java/android/content/Context.java
+++ b/core/java/android/content/Context.java
@@ -2877,11 +2877,10 @@
 
     /**
      * Use with {@link #getSystemService} to retrieve a {@link
-     * android.app.usage.UsageStatsManager} for interacting with the status bar.
+     * android.app.usage.UsageStatsManager} for querying device usage stats.
      *
      * @see #getSystemService
      * @see android.app.usage.UsageStatsManager
-     * @hide
      */
     public static final String USAGE_STATS_SERVICE = "usagestats";