Fix a couple of scroll-related issues:

remoting/webapp/client_session.js

Index: remoting/webapp/client_session.js
diff --git a/remoting/webapp/client_session.js b/remoting/webapp/client_session.js
index d4c570845703086bb65374a97eb747aa5936b5e9..05882cbefd6e0c59d4b02bb3179bde1f02818bb9 100644
--- a/remoting/webapp/client_session.js
+++ b/remoting/webapp/client_session.js
@@ -585,6 +585,7 @@ remoting.ClientSession.prototype.removePlugin = function() {
   } else {
     remoting.toolbar.setClientSession(null);
   }
+  document.body.classList.remove('connected');
 
   // Remove mediasource-rendering class from the container - this will also
   // hide the <video> element.
@@ -972,6 +973,7 @@ remoting.ClientSession.prototype.onConnectionStatusUpdate_ =
     } else {
       remoting.toolbar.setClientSession(this);
     }
+    document.body.classList.add('connected');
 
     this.container_.addEventListener('mousemove',
                                      this.updateMouseCursorPosition_,