[devtools] Return empty array from DOMNode.children() rather than null.

Source/devtools/front_end/DOMAgent.js

Index: Source/devtools/front_end/DOMAgent.js
diff --git a/Source/devtools/front_end/DOMAgent.js b/Source/devtools/front_end/DOMAgent.js
index 45467bc785d2b124fa86413c1df121a4feaaf940..c1795aa15e1627c9e80238ad286f1d7903ea2790 100644
--- a/Source/devtools/front_end/DOMAgent.js
+++ b/Source/devtools/front_end/DOMAgent.js
@@ -138,7 +138,7 @@ WebInspector.DOMNode.prototype = {
      */
     children: function()
     {
-        return this._children ? this._children.slice() : null;
+        return this._children ? this._children.slice() : [];

[pfeldman, 2013/10/09 05:41:06]

This is intentionally null. We should instead do:

children: function()
{
    if (!this._children)
        throw new Error("Requesting children prior to getting them from
backend");
    return this._children;
}

Client should only use this method when they are confident node has already
received children asynchronously and they can proceed with synchronous
operation. This applies to ElementsTreeOutline call sites. If that is not the
case, please file a bug.

     },
 
     /**