add accessibility descriptions/events

    Bug: 4979091
    added content descriptions to the image buttons
    send event for screen transition

Change-Id: I403fe8504cace4aa84a5b1c6ca18f6c10fc9be34
diff --git a/res/layout/nav_tab_view.xml b/res/layout/nav_tab_view.xml
index dbf9494..6330357 100644
--- a/res/layout/nav_tab_view.xml
+++ b/res/layout/nav_tab_view.xml
@@ -46,6 +46,7 @@
             android:layout_gravity="center_vertical"
             android:layout_width="wrap_content"
             android:layout_height="match_parent"
+            android:contentDescription="@string/accessibility_button_closetab"
             style="@style/HoloButton" />
     </LinearLayout>
     <ImageView