Expose Intent#EXTRA_REASON as a SystemApi.

It's expected to be set with ACTION_FACTORY_RESET intents, and this
action was exposed as a @SystemApi in b/32974361.

Change-Id: Ib29ffb8d62460eb4ec0208076331bbba3272f290
Fixes: 67751036
Test: Just TreeHugger; no functional changes
diff --git a/core/java/android/content/Intent.java b/core/java/android/content/Intent.java
index e47de75..dd729a3 100644
--- a/core/java/android/content/Intent.java
+++ b/core/java/android/content/Intent.java
@@ -3444,11 +3444,12 @@
     /**
      * A broadcast action to trigger a factory reset.
      *
-     * <p> The sender must hold the {@link android.Manifest.permission#MASTER_CLEAR} permission.
+     * <p>The sender must hold the {@link android.Manifest.permission#MASTER_CLEAR} permission. The
+     * reason for the factory reset should be specified as {@link #EXTRA_REASON}.
      *
      * <p>Not for use by third-party applications.
      *
-     * @see #EXTRA_FORCE_MASTER_CLEAR
+     * @see #EXTRA_FORCE_FACTORY_RESET
      *
      * {@hide}
      */
@@ -4827,7 +4828,13 @@
     /** @hide */
     public static final int EXTRA_TIME_PREF_VALUE_USE_LOCALE_DEFAULT = 2;
 
-    /** {@hide} */
+    /**
+     * Intent extra: the reason that the operation associated with this intent is being performed.
+     *
+     * <p>Type: String
+     * @hide
+     */
+    @SystemApi
     public static final String EXTRA_REASON = "android.intent.extra.REASON";
 
     /**