Add missing popup i18n messages

ext/src/_locales/en/messages.json

@@ -15,6 +15,12 @@
   , "popupMediaTypeScreen": {
         "message": "Screen"
     }
+  , "popupMediaSelectCastLabel": {
+        "message": "Cast"
+    }
+  , "popupMediaSelectToLabel": {
+        "message": "to:"
+    }
   , "popupCastButtonLabel": {
         "message": "Cast"
     }

ext/src/receiverSelectorManager/selectorManagers/NativeMacReceiverSelectorManager.ts

@@ -61,6 +61,8 @@ class NativeMacReceiverSelectorManager
               , i18n_mediaTypeApp: _("popupMediaTypeApp")
               , i18n_mediaTypeTab: _("popupMediaTypeTab")
               , i18n_mediaTypeScreen: _("popupMediaTypeScreen")
+              , i18n_mediaSelectCastLabel: _("popupMediaSelectCastLabel")
+              , i18n_mediaSelectToLabel: _("popupMediaSelectToLabel")
             })
         });
     }

ext/src/ui/popup/index.tsx

@@ -97,7 +97,7 @@ class PopupApp extends Component<{}, PopupAppState> {
         return (
             <div>
                 <div className="media-select">
-                    Cast
+                    { _("popupMediaSelectCastLabel") }
                     <select value={ this.state.mediaType }
                             onChange={ this.onSelectChange }
                             className="media-select-dropdown">
@@ -115,7 +115,7 @@ class PopupApp extends Component<{}, PopupAppState> {
                             { _("popupMediaTypeScreen") }
                         </option>
                     </select>
-                    to:
+                    { _("popupMediaSelectToLabel") }
                 </div>
                 <ul className="receivers">
                     { this.state.receivers.map((receiver, i) => {