Use optional default value syntax in Selection.idl

Source/core/editing/DOMSelection.cpp

Index: Source/core/editing/DOMSelection.cpp
diff --git a/Source/core/editing/DOMSelection.cpp b/Source/core/editing/DOMSelection.cpp
index 68f9d09e290a877e6eef3d1efb166a3d2593241d..6012b131dbfb49621d2f7980ef49dffd783e7777 100644
--- a/Source/core/editing/DOMSelection.cpp
+++ b/Source/core/editing/DOMSelection.cpp
@@ -218,11 +218,6 @@ void DOMSelection::collapse(Node* node, int offset, ExceptionState& exceptionSta
     m_frame->selection().setSelectedRange(range.get(), DOWNSTREAM, m_frame->selection().isDirectional() ? FrameSelection::Directional : FrameSelection::NonDirectional);
 }
 
-void DOMSelection::collapse(Node* node, ExceptionState& exceptionState)
-{
-    collapse(node, 0, exceptionState);
-}
-
 void DOMSelection::collapseToEnd(ExceptionState& exceptionState)
 {
     if (!m_frame)
@@ -358,13 +353,6 @@ void DOMSelection::extend(Node* node, int offset, ExceptionState& exceptionState
     m_frame->selection().setExtent(VisiblePosition(createLegacyEditingPosition(node, offset), DOWNSTREAM));
 }
 
-void DOMSelection::extend(Node* node, ExceptionState& exceptionState)
-{
-    // This default value implementation differs from the spec, which says |offset| is not optional.
-    // FIXME: Specify this default value in Selection.idl.
-    extend(node, 0, exceptionState);
-}
-
 PassRefPtrWillBeRawPtr<Range> DOMSelection::getRangeAt(int index, ExceptionState& exceptionState)
 {
     if (!m_frame)