[AppRemoting] Implement ConnectionDroppedDialog.

remoting/webapp/app_remoting/js/app_remoting_activity.js

Index: remoting/webapp/app_remoting/js/app_remoting_activity.js
diff --git a/remoting/webapp/app_remoting/js/app_remoting_activity.js b/remoting/webapp/app_remoting/js/app_remoting_activity.js
index 19ec51208f6b249e4b49e3cb134b428b1ed21a2b..0ac60af30d30ea5dcff8a45c5eaa929c7d0ac341 100644
--- a/remoting/webapp/app_remoting/js/app_remoting_activity.js
+++ b/remoting/webapp/app_remoting/js/app_remoting_activity.js
@@ -180,9 +180,8 @@ remoting.AppRemotingActivity.prototype.onDisconnected = function(error) {
   if (error.isNone()) {
     chrome.app.window.current().close();
   } else {
-    this.showErrorMessage_(error);
+    this.onConnectionDropped_();
   }
-  this.cleanup_();
 };
 
 /**
@@ -194,6 +193,28 @@ remoting.AppRemotingActivity.prototype.onConnectionFailed = function(error) {
   this.cleanup_();
 };
 
+/** @private */
+remoting.AppRemotingActivity.prototype.onConnectionDropped_ = function() {

[Jamie, 2015/05/20 02:20:37]

I think there's value in passing the error into here. We should at least log it,
and maybe surface it in the dialog as well (perhaps behind a "more information"
expander).

[kelvinp, 2015/05/20 18:13:00]

The error is already logged in the earlier stack (in clientSession.js)  As
discussed, leaving the dialog as is for now.

+  var rootElement = /** @type {HTMLDialogElement} */ (
+      document.getElementById('connection-dropped-dialog'));
+  var dialog = new remoting.Html5ModalDialog(
+      rootElement, rootElement.querySelector('.restart-button'),
+      rootElement.querySelector('.close-button'));
+  var Result = remoting.MessageDialog.Result;

[Jamie, 2015/05/20 02:20:37]

I'm surprised that this assignment works as far as using it as a JSCompile type
is concerned. In any case, it doesn't seem to result in shorter code, so I would
just write out the type longhand in the two places you're using it.

[kelvinp, 2015/05/20 18:12:59]

Done.

+  var that = this;
+
+  dialog.show().then(function(/** Result */ result) {
+    if (result === Result.PRIMARY) {
+      // Hide the desktop window before tearing down the plugin.

[Jamie, 2015/05/20 02:20:37]

This comment doesn't seem to be accurate.

[kelvinp, 2015/05/20 18:13:00]

Maybe I need to phrase it better.  By calling setDesktopRect to an empty array,
we are telling the windowshape to not render any desktop window of the remote
application. 

+      remoting.windowShape.setDesktopRects([]);
+      that.cleanup_();
+      that.start();
+    } else {
+      chrome.app.window.current().close();
+    }
+  });
+};
+
 /**
  * @param {!remoting.Error} error The error to be localized and displayed.
  * @private