Make THEATER_MODE_ON setting a system api.

This will allow an unbundled home to continue accessing this property.

Bug: 19043538
Change-Id: I845a8726e617ca7b6f7f7347a0ac5aa0620d6658
diff --git a/api/system-current.txt b/api/system-current.txt
index 39685ae..45e8f87 100644
--- a/api/system-current.txt
+++ b/api/system-current.txt
@@ -26872,6 +26872,7 @@
     field public static final java.lang.String SHOW_PROCESSES = "show_processes";
     field public static final java.lang.String STAY_ON_WHILE_PLUGGED_IN = "stay_on_while_plugged_in";
     field public static final java.lang.String SYS_PROP_SETTING_VERSION = "sys.settings_global_version";
+    field public static final java.lang.String THEATER_MODE_ON = "theater_mode_on";
     field public static final java.lang.String TRANSITION_ANIMATION_SCALE = "transition_animation_scale";
     field public static final java.lang.String USB_MASS_STORAGE_ENABLED = "usb_mass_storage_enabled";
     field public static final java.lang.String USE_GOOGLE_MAIL = "use_google_mail";
diff --git a/core/java/android/provider/Settings.java b/core/java/android/provider/Settings.java
index 838686a..92349338 100644
--- a/core/java/android/provider/Settings.java
+++ b/core/java/android/provider/Settings.java
@@ -5101,6 +5101,7 @@
          * Whether Theater Mode is on.
          * {@hide}
          */
+        @SystemApi
         public static final String THEATER_MODE_ON = "theater_mode_on";
 
         /**