MediaRouter: Add missing content description for album art

Bug: 28292892
Change-Id: I5f2d3204df622b6400bda36b28de38bb966fc7a6
diff --git a/v7/mediarouter/res/layout/mr_controller_material_dialog_b.xml b/v7/mediarouter/res/layout/mr_controller_material_dialog_b.xml
index 94ad82b..0147fe3 100644
--- a/v7/mediarouter/res/layout/mr_controller_material_dialog_b.xml
+++ b/v7/mediarouter/res/layout/mr_controller_material_dialog_b.xml
@@ -61,6 +61,7 @@
                        android:scaleType="fitXY"
                        android:background="?attr/colorPrimary"
                        android:layout_gravity="top"
+                       android:contentDescription="@string/mr_controller_album_art"
                        android:visibility="gone" />
             <LinearLayout android:layout_width="fill_parent"
                           android:layout_height="wrap_content"
diff --git a/v7/mediarouter/res/values/strings.xml b/v7/mediarouter/res/values/strings.xml
index fad0408..b6a949a 100644
--- a/v7/mediarouter/res/values/strings.xml
+++ b/v7/mediarouter/res/values/strings.xml
@@ -52,6 +52,9 @@
     <!-- Content description for accessibility (not shown on the screen): group collapse button. Pressing button hides group members of a selected route group. [CHAR LIMIT=NONE] -->
     <string name="mr_controller_collapse_group">Collapse</string>
 
+    <!-- Content description for accessibility (not shown on the screen): album art button. Clicking on the album art takes user to a predefined activity per media app. [CHAR LIMIT=50] -->
+    <string name="mr_controller_album_art">Album art</string>
+
     <!-- Placeholder text to show when no media have been selected for playback. [CHAR LIMIT=50] -->
     <string name="mr_controller_no_media_selected">No media selected</string>