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_screen.xml b/res/layout/nav_screen.xml
index b4e1f15..8ff4be3 100644
--- a/res/layout/nav_screen.xml
+++ b/res/layout/nav_screen.xml
@@ -41,6 +41,7 @@
             android:paddingRight="16dip"
             style="@style/HoloButton"
             android:gravity="center_vertical"
+            android:contentDescription="@string/accessibility_button_newtab"
             android:src="@drawable/ic_new_window_holo_dark" />
         <ImageButton
             android:id="@+id/newincognito"
@@ -50,6 +51,7 @@
             android:paddingRight="16dip"
             style="@style/HoloButton"
             android:gravity="center_vertical"
+            android:contentDescription="@string/accessibility_button_newincognitotab"
             android:src="@drawable/ic_new_incognito_holo_dark" />
         <ImageButton
             android:id="@+id/bookmarks"
@@ -57,6 +59,7 @@
             android:layout_height="match_parent"
             android:paddingLeft="16dip"
             android:paddingRight="16dip"
+            android:contentDescription="@string/accessibility_button_bookmarks"
             android:src="@drawable/ic_bookmarks_history_holo_dark"
             style="@style/HoloButton" />
         <ImageButton
@@ -67,6 +70,7 @@
             android:paddingRight="16dip"
             style="@style/HoloButton"
             android:gravity="center_vertical"
+            android:contentDescription="@string/accessibility_button_more"
             android:src="@*android:drawable/ic_menu_moreoverflow_normal_holo_dark" />
     </LinearLayout>
 </RelativeLayout>