ui: Add debug flag to show composited layer borders in ChromeOS UI.

ash/debug.cc

Index: ash/debug.cc
diff --git a/ash/debug.cc b/ash/debug.cc
index fe3788961c765ac67650c742f562ffa03c434324..7a855443cc1740dfcbf88e7cc791e476725fcbba 100644
--- a/ash/debug.cc
+++ b/ash/debug.cc
@@ -15,13 +15,13 @@ namespace debug {
 void ToggleShowDebugBorders() {
   aura::Window::Windows root_windows =
       Shell::GetInstance()->GetAllRootWindows();
-  std::unique_ptr<bool> value;
+  std::unique_ptr<cc::DebugBorderTypes> value;
   for (aura::Window::Windows::iterator it = root_windows.begin();
        it != root_windows.end(); ++it) {
     ui::Compositor* compositor = (*it)->GetHost()->compositor();
     cc::LayerTreeDebugState state = compositor->GetLayerTreeDebugState();
     if (!value.get())
-      value.reset(new bool(!state.show_debug_borders));
+      value.reset(new cc::DebugBorderTypes(state.show_debug_borders.flip()));
     state.show_debug_borders = *value.get();
     compositor->SetLayerTreeDebugState(state);
   }