Bug 332797, Erroneous tree.columns[0] undefined property warning, patch by Andrew Miller <ak.miller@auckland.ac.nz>, r=enndeakin, sr=jst

layout/xul/base/src/tree/public/nsITreeColumns.idl

@@ -73,7 +73,7 @@ interface nsITreeColumn : nsISupports
 
 interface nsITreeBoxObject;
 
-[scriptable, uuid(fcc7b6b5-f7d7-4e57-abd1-080602deb21d)]
+[scriptable, uuid(f8a8d6b4-6788-438d-9009-7142798767ab)]
 interface nsITreeColumns : nsISupports
 {
   /**
@@ -86,6 +86,12 @@ interface nsITreeColumns : nsISupports
    */
   readonly attribute long count;
 
+  /**
+   * An alias for count (for the benefit of scripts which treat this as an
+   * array).
+   */
+  readonly attribute long length;
+
   /**
    * Get the first/last column.
    */

layout/xul/base/src/tree/src/nsTreeColumns.cpp

@@ -306,6 +306,12 @@ nsTreeColumns::GetCount(PRInt32* _retval)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsTreeColumns::GetLength(PRInt32* _retval)
+{
+  return GetCount(_retval);
+}
+
 NS_IMETHODIMP
 nsTreeColumns::GetFirstColumn(nsITreeColumn** _retval)
 {