Fix build (again).

Another set of strings that needed to be localized but were
missed in 4fe89883c2.

Change-Id: Ibb08df992129361578aeb1c556f4d965ab3404c2

samples/SupportDesignDemos/res/layout/design_tabs_viewpager.xml

@@ -54,13 +54,13 @@
                 android:id="@+id/btn_add_tab"
                 android:layout_width="wrap_content"
                 android:layout_height="wrap_content"
-                android:text="Add Tab"/>
+                android:text="@string/add_tab"/>
 
         <Button
                 android:id="@+id/btn_remove_tab"
                 android:layout_width="wrap_content"
                 android:layout_height="wrap_content"
-                android:text="Remove Tab"/>
+                android:text="@string/remove_tab"/>
 
     </LinearLayout>
 

samples/SupportDesignDemos/res/values/strings.xml

@@ -27,4 +27,7 @@
     <string name="tabs_gravity_center">Center</string>
     <string name="tabs_gravity_fill">Fill</string>
 
+    <string name="add_tab">Add tab</string>
+    <string name="remove_tab">Remove tab</string>
+
 </resources>