Add flag to enable immersive fullscreen for v2 apps

ash/wm/window_state_delegate.cc

Index: ash/wm/window_state_delegate.cc
diff --git a/ash/wm/window_state_delegate.cc b/ash/wm/window_state_delegate.cc
index 00040735ea4d4d7fb84ddb47fe2bba1ac0efe764..cc1cc5180961a3c3ee25f1825f210798d6e93a16 100644
--- a/ash/wm/window_state_delegate.cc
+++ b/ash/wm/window_state_delegate.cc
@@ -13,7 +13,11 @@ WindowStateDelegate::WindowStateDelegate() {
 WindowStateDelegate::~WindowStateDelegate() {
 }
 
-bool WindowStateDelegate::ToggleFullscreen(WindowState* window_state) {
+bool WindowStateDelegate::EnterImmersiveFullscreen(WindowState* window_state) {
+  return false;
+}
+
+bool WindowStateDelegate::ExitFullscreen(WindowState* window_state) {
   return false;
 }