Pass the output area object in events specific to the output area.

Also, add a new event triggered right before the output area is cleared. This is useful if an output renderer has cleanup work to do before the DOM element is removed off of the page.

notebook/static/notebook/js/outputarea.js

@@ -348,7 +348,7 @@ define([
             this._needs_height_reset = false;
         }
 
-        this.element.trigger('resizeOutput');
+        this.element.trigger('resizeOutput', {output_area: this});
     };
 
     OutputArea.prototype.create_output_area = function () {
@@ -451,7 +451,7 @@ define([
         }
 
         // Notify others of changes.
-        this.element.trigger('changed');
+        this.element.trigger('changed', {output_area: this});
     };
 
 
@@ -965,11 +965,12 @@ define([
             // Remove load event handlers from img tags because we don't want
             // them to fire if the image is never added to the page.
             this.element.find('img').off('load');
+            this.element.trigger('clearing', {output_area: this});
             this.element.html("");
 
             // Notify others of changes.
-            this.element.trigger('changed');
-            this.element.trigger('cleared');
+            this.element.trigger('changed', {output_area: this});
+            this.element.trigger('cleared', {output_area: this});
             
             this.outputs = [];
             this._display_id_targets = {};