Pass column as 4th argument to WorkerGlobalScope.onerror handler

Source/core/dom/ErrorEvent.idl

Index: Source/core/dom/ErrorEvent.idl
diff --git a/Source/core/dom/ErrorEvent.idl b/Source/core/dom/ErrorEvent.idl
index 612a97008014335d3c1679ce1dfbf5afdb2a9ffb..21195e9a9c0f90402e907ac8df2dd1c55aa36149 100644
--- a/Source/core/dom/ErrorEvent.idl
+++ b/Source/core/dom/ErrorEvent.idl
@@ -34,5 +34,9 @@
     [InitializedByEventConstructor] readonly attribute DOMString message;
     [InitializedByEventConstructor] readonly attribute DOMString filename;
     [InitializedByEventConstructor] readonly attribute unsigned long lineno;
+
+    // FIXME: Part of the specification but not exposed yet.
+    // No other browser seems to support it (except IE10 as 'colno').
+    // [InitializedByEventConstructor] readonly attribute unsigned long column;
 };