[Chromoting] Show any startup errors in the LoadingWindow.

remoting/webapp/base/js/message_window.js

Index: remoting/webapp/base/js/message_window.js
diff --git a/remoting/webapp/base/js/message_window.js b/remoting/webapp/base/js/message_window.js
index f110e6f659a6162dd852f061f2497cb45bd0187d..3d8edaea248dd91a74f91a472b857cfd0a619e33 100644
--- a/remoting/webapp/base/js/message_window.js
+++ b/remoting/webapp/base/js/message_window.js
@@ -62,6 +62,21 @@ MessageWindowImpl.prototype.initButton_ =
 };
 
 /**
+ * Updates the button label text.
+ * Hides the button if the label is null or undefined.
+ *
+ * @param{HTMLElement} button
+ * @param{?string} label
+ * @private
+ */
+MessageWindowImpl.prototype.updateButton_ = function(button, label) {
+  if (label) {
+    button.innerText = label;
+  }
+  button.hidden = !Boolean(label);
+};
+
+/**
  * Event-handler callback, invoked when the parent window supplies the
  * message content.
  *
@@ -77,8 +92,8 @@ MessageWindowImpl.prototype.onMessage_ = function(event) {
       var message = /** @type {string} */ (event.data['message']);
       var infobox = /** @type {string} */ (event.data['infobox']);
       var buttonLabel = /** @type {string} */ (event.data['buttonLabel']);
-      /** @type {string} */
-      var cancelButtonLabel = (event.data['cancelButtonLabel']);
+      var cancelButtonLabel = /** @type {string} */
+          (event.data['cancelButtonLabel']);
       var showSpinner = /** @type {boolean} */ (event.data['showSpinner']);
       if (typeof(messageId) != 'number' ||
           typeof(title) != 'string' ||
@@ -136,14 +151,37 @@ MessageWindowImpl.prototype.onMessage_ = function(event) {
 
     case 'update_message':

[Jamie, 2015/05/09 01:17:00]

How about renaming this message 'update' and having it take the same parameters
as show, although with all of them optional to indicate "no change"? It would
mean that a lot of the code could be shared with the 'show' message, and any
parameter could be changed on the fly, rather than these select few.

[garykac, 2015/05/11 21:34:16]

Done.

       var message = /** @type {string} */ (event.data['message']);
+      var buttonLabel = /** @type {string} */ (event.data['buttonLabel']);
+      var cancelButtonLabel = /** @type {string} */
+          (event.data['cancelButtonLabel']);
+      var showSpinner = /** @type {boolean} */ (event.data['showSpinner']);
+      // The update_message may leave the buttonLabel, cancelButtonLabel and
+      // showSpinner values undefined to have them retain their current values.
       if (typeof(message) != 'string') {
         console.log('Bad update_message message:', event.data);
         break;
       }
 
+      var button = document.getElementById('button-primary');
+      var cancelButton = document.getElementById('button-secondary');
       var messageDiv = document.getElementById('message');
+
       messageDiv.innerText = message;
 
+      // If showSpinner was not specified, then don't change its state.
+      if (typeof(showSpinner) == 'boolean') {
+        if (showSpinner) {
+          messageDiv.classList.add('waiting');
+          messageDiv.classList.add('prominent');
+        } else {
+          messageDiv.classList.remove('waiting');
+          messageDiv.classList.remove('prominent');
+        }
+      }
+
+      this.updateButton_(button, buttonLabel);
+      this.updateButton_(cancelButton, cancelButtonLabel);
+
       base.resizeWindowToContent(true);
       break;