Add settings for the assist gesture.

Availability of the gesture is gated by a new FeatureProvider.

Test: make -j RunSettingsRoboTests; manual test on
      supported/unsupported configurations.

Change-Id: I3529367a73e33370d5112b91d5144293ffa7fa22
diff --git a/res/xml/gesture_settings.xml b/res/xml/gesture_settings.xml
index 8954916..808c9b2 100644
--- a/res/xml/gesture_settings.xml
+++ b/res/xml/gesture_settings.xml
@@ -20,6 +20,13 @@
     settings:keywords="@string/keywords_gesture">
 
     <com.android.settings.gestures.GesturePreference
+        android:key="gesture_assist"
+        android:title="@string/assist_gesture_title"
+        android:summary="@string/assist_gesture_summary"
+        settings:animation="@raw/gesture_assist"
+        settings:preview="@drawable/gesture_assist"/>
+
+    <com.android.settings.gestures.GesturePreference
         android:key="gesture_swipe_down_fingerprint"
         android:title="@string/fingerprint_swipe_for_notifications_title"
         android:summary="@string/fingerprint_swipe_for_notifications_summary"
@@ -54,4 +61,4 @@
         settings:animation="@raw/gesture_ambient_lift"
         settings:preview="@drawable/gesture_ambient_lift"/>
 
-</PreferenceScreen>
\ No newline at end of file
+</PreferenceScreen>