[Media Router WebUI] Set titles for buttons.

chrome/app/media_router_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Media Router-specific strings (included from generated_resources.grd). -->
 <grit-part>
   <!-- General -->
   <message name="IDS_MEDIA_ROUTER_TITLE" desc="Title of a dialog offering possible actions for Media Router, which enables users to mirror individual tabs or desktop as well as cast content to a device.">
     Media Router
   </message>
   <message name="IDS_MEDIA_ROUTER_ICON_TOOLTIP_TEXT" desc="Tooltip for the Media Router Action icon, which appears in the toolbar. The tooltip appears on mouseover of the icon.">
    Display on another screen
   </message>
   <message name="IDS_MEDIA_ROUTER_MENU_ITEM_TITLE" desc="Title of menu item for Media Router, which appears in the overflow menu and page contextual menus.">
     Cast...
   </message>
   <message name="IDS_MEDIA_ROUTER_LEARN_MORE" desc="Text of a menu item or link which, on click, opens a page with more information or relevant help center page.">
    Learn more
   </message>
 
+  <!-- Button Titles -->
+  <message name="IDS_MEDIA_ROUTER_BACK_BUTTON_TITLE" desc="Back button title, which is spoken when a screen reader is being used.">
+    Back
+  </message>
+  <message name="IDS_MEDIA_ROUTER_CLOSE_BUTTON_TITLE" desc="Close button title, which is spoken when a screen reader is being used.">
+    Close
+  </message>
+  <message name="IDS_MEDIA_ROUTER_DROP_DOWN_BUTTON_TITLE" desc="Drop down button title, which is spoken when a screen reader is being used.">
+    Drop down
+  </message>
+  <message name="IDS_MEDIA_ROUTER_SEARCH_BUTTON_TITLE" desc="Search button title, which is spoken when a screen reader is being used.">
+    Search
+  </message>
+
   <!-- Cast Modes -->
   <message name="IDS_MEDIA_ROUTER_AUTO_CAST_MODE" desc="Title for auto cast mode that appears as the header of a list of devices. This represents the mode that will be initially shown, if the list of sinks supports more than one of the cast modes below. Note that auto mode is not a real cast mode and merely serves as a proxy for the other cast modes. This is NOT shown as a dropdown option.">
     Cast to
   </message>
   <message name="IDS_MEDIA_ROUTER_DEFAULT_CAST_MODE" desc="Title for the default cast mode, which is used when the host is cast enabled. This is shown as a dropdown option, and if selected, also appears as the header of a list of devices.">
     Cast <ph name="HOST_NAME">$1<ex>google.com</ex></ph>
   </message>
   <message name="IDS_MEDIA_ROUTER_DESKTOP_MIRROR_CAST_MODE" desc="Title for the desktop mirror cast mode. This is shown as a dropdown option, and if selected, also appears as the header of a list of devices.">
     Cast desktop
   </message>
@@ skipping 88 matching lines @@
   </message>
 
   <!-- Sink Search -->
   <message name="IDS_MEDIA_ROUTER_SEARCH_LABEL" desc="Label for search input in sink list.">
     Search
   </message>
   <message name="IDS_MEDIA_ROUTER_SEARCH_NO_MATCHES" desc="Text to display when there are no sinks matching the user input search text.">
     No matches
   </message>
 </grit-part>