[build-fix] [gcc 4.6.*] Use iterator instead of const_iterator while using std::map::erase(...)

mojo/services/window_manager/window_manager_app.cc

Index: mojo/services/window_manager/window_manager_app.cc
diff --git a/mojo/services/window_manager/window_manager_app.cc b/mojo/services/window_manager/window_manager_app.cc
index f8380dd436733ddf827374875a40ac4fc3a492ac..bb096f5c9e3ec21df2469e34db0a0d9bb1e16e54 100644
--- a/mojo/services/window_manager/window_manager_app.cc
+++ b/mojo/services/window_manager/window_manager_app.cc
@@ -261,7 +261,7 @@ void WindowManagerApp::RegisterSubtree(view_manager::Id id,
 
 void WindowManagerApp::UnregisterSubtree(view_manager::Id id) {
   view_manager::Node* node = view_manager_->GetNodeById(id);
-  NodeIdToWindowMap::const_iterator it = node_id_to_window_map_.find(id);
+  NodeIdToWindowMap::iterator it = node_id_to_window_map_.find(id);
   DCHECK(it != node_id_to_window_map_.end());
   scoped_ptr<aura::Window> window(it->second);
   node_id_to_window_map_.erase(it);