[Harmony Cast Dialog] Change the header text from "Cast to" to "Cast"

Bug: 878541
Change-Id: I2501fa03d737154697346a76c1a7e20758debd7f
Reviewed-on: https://chromium-review.googlesource.com/1214075Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590018}

chrome/app/media_router_strings.grdp

@@ -11,6 +11,9 @@
   <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.">
     &amp;Cast...
   </message>
+  <message name="IDS_MEDIA_ROUTER_CAST_DIALOG_TITLE" desc="Title of the dialog with which users can cast media contents to Chromecast and other devices. This text is shown at the top of the dialog on its own line, and should be considered a verb.">
+    Cast
+  </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.">

chrome/browser/ui/views/media_router/media_router_views_ui.cc

@@ -105,7 +105,7 @@ void MediaRouterViewsUI::OnRoutesUpdated(
 
 void MediaRouterViewsUI::UpdateSinks() {
   model_.set_dialog_header(
-      l10n_util::GetStringUTF16(IDS_MEDIA_ROUTER_AUTO_CAST_MODE));
+      l10n_util::GetStringUTF16(IDS_MEDIA_ROUTER_CAST_DIALOG_TITLE));
   std::vector<UIMediaSink> media_sinks;
   for (const MediaSinkWithCastModes& sink : GetEnabledSinks()) {
     auto route_it = std::find_if(