[Media Router WebUI] Update arrow drop title text to be more descriptive.

chrome/app/media_router_strings.grdp

Index: chrome/app/media_router_strings.grdp
diff --git a/chrome/app/media_router_strings.grdp b/chrome/app/media_router_strings.grdp
index b668b80c13052f7ef293a9474775c5284b2bf068..207746833b8a7a58f56fdb7946089aa3afe02c81 100644
--- a/chrome/app/media_router_strings.grdp
+++ b/chrome/app/media_router_strings.grdp
@@ -22,12 +22,15 @@
   <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>
+  <message name="IDS_MEDIA_ROUTER_VIEW_CAST_MODE_LIST_BUTTON_TITLE" desc="View cast modes list button title, which is spoken when a screen reader is being used.">
+    View cast mode list
+  </message>
+  <message name="IDS_MEDIA_ROUTER_VIEW_DEVICE_LIST_BUTTON_TITLE" desc="View device list button title, which is spoken when a screen reader is being used.">
+    View device list
+  </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.">