[cc] Fix crash when adding a child layer to its own parent.

cc/layer.cc

Index: cc/layer.cc
diff --git a/cc/layer.cc b/cc/layer.cc
index 29fe62a8bfa0b955ca2ced34595e9b4de3e93edb..afc8627ad87fdc50b8e3a466fc3762d168eae5da 100644
--- a/cc/layer.cc
+++ b/cc/layer.cc
@@ -155,11 +155,11 @@ void Layer::addChild(scoped_refptr<Layer> child)
 
 void Layer::insertChild(scoped_refptr<Layer> child, size_t index)
 {
-    index = min(index, m_children.size());
     child->removeFromParent();
     child->setParent(this);
     child->m_stackingOrderChanged = true;
 
+    index = min(index, m_children.size());
     LayerList::iterator iter = m_children.begin();
     m_children.insert(iter + index, child);
     setNeedsCommit();