Update shelf spacing in Chrome OS according to the MD specs

ash/root_window_controller_unittest.cc

Index: ash/root_window_controller_unittest.cc
diff --git a/ash/root_window_controller_unittest.cc b/ash/root_window_controller_unittest.cc
index 58ccc2e0fc3392ac5436ee3b369fdbfd92b32074..bac63b911346c9f862149e3dc162363fdda426a0 100644
--- a/ash/root_window_controller_unittest.cc
+++ b/ash/root_window_controller_unittest.cc
@@ -205,7 +205,7 @@ TEST_F(RootWindowControllerTest, MoveWindows_Basic) {
             normal->GetNativeView()->GetBoundsInRootWindow().ToString());
 
   // Maximized area on primary display has 3px (given as
-  // kAutoHideSize in shelf_layout_manager.cc) inset at the bottom.
+  // kAutoHideSize in shelf_constants.cc) inset at the bottom.
 
   // First clear fullscreen status, since both fullscreen and maximized windows
   // share the same desktop workspace, which cancels the shelf status.