Added msg_throttle sync=True widget traitlet

IPython/html/static/notebook/js/widgets/widget.js

@@ -34,7 +34,6 b' function(WidgetManager, _, Backbone){'
             this.widget_manager = widget_manager;
             this._buffered_state_diff = {};
             this.pending_msgs = 0;
-            this.msg_throttle = 3;
             this.msg_buffer = null;
             this.key_value_lock = null;
             this.id = model_id;
@@ -110,7 +109,7 b' function(WidgetManager, _, Backbone){'
                     // Send buffer if this message caused another message to be
                     // throttled.
                     if (this.msg_buffer !== null &&
-                        this.msg_throttle === this.pending_msgs) {
+                        this.get('msg_throttle') || 3 === this.pending_msgs) {
                         var data = {method: 'backbone', sync_method: 'update', sync_data: this.msg_buffer};
                         this.comm.send(data, callbacks);
                         this.msg_buffer = null;
@@ -179,7 +178,7 b' function(WidgetManager, _, Backbone){'
                 var callbacks = options.callbacks || this.callbacks();
 
                 // Check throttle.
-                if (this.pending_msgs >= this.msg_throttle) {
+                if (this.pending_msgs >= this.get('msg_throttle') || 3) {
                     // The throttle has been exceeded, buffer the current msg so
                     // it can be sent once the kernel has finished processing 
                     // some of the existing messages.

IPython/html/widgets/widget.py

@@ -17,7 +17,7 b' from contextlib import contextmanager'
 from IPython.core.getipython import get_ipython
 from IPython.kernel.comm import Comm
 from IPython.config import LoggingConfigurable
-from IPython.utils.traitlets import Unicode, Dict, Instance, Bool, List, Tuple
+from IPython.utils.traitlets import Unicode, Dict, Instance, Bool, List, Tuple, Int
 from IPython.utils.py3compat import string_types
 
 #-----------------------------------------------------------------------------
@@ -103,6 +103,8 b' class Widget(LoggingConfigurable):'
     _comm = Instance('IPython.kernel.comm.Comm')
     
     closed = Bool(False)
+    msg_throttle = Int(3, sync=True, help="""Maximum number of msgs the 
+        front-end can send before receiving an idle msg from the back-end.""")
     
     keys = List()
     def _keys_default(self):