Allow MessageWindow callers to specify a minimum width.

remoting/webapp/base/js/message_window_helper.js

Index: remoting/webapp/base/js/message_window_helper.js
diff --git a/remoting/webapp/base/js/message_window_helper.js b/remoting/webapp/base/js/message_window_helper.js
index 90267add4dc60a0b1e5e9df92a0d91d11d8361eb..f6657577c4982894d44f22afa5bd43c2f5e1ea22 100644
--- a/remoting/webapp/base/js/message_window_helper.js
+++ b/remoting/webapp/base/js/message_window_helper.js
@@ -38,6 +38,9 @@ remoting.MessageWindowOptions = function() {
 
   /** @type {string} */
   this.frame = '';
+
+  /** @type {number} */
+  this.minimumWidth = 0;
 };
 
 /**
@@ -96,7 +99,7 @@ remoting.MessageWindow = function(options) {
 
   var windowAttributes = {
     bounds: {
-      width: 400,
+      width: options.minimumWidth || 400,
       height: 100
     },
     resizable: false,