Add flag to enable immersive fullscreen for v2 apps

ash/wm/window_state.cc

Index: ash/wm/window_state.cc
diff --git a/ash/wm/window_state.cc b/ash/wm/window_state.cc
index 1a06a58da1bb0a0b876bb2c64457d10d234feab1..c7b13caa5842ac6e0602e1355d6c70e882451b10 100644
--- a/ash/wm/window_state.cc
+++ b/ash/wm/window_state.cc
@@ -170,18 +170,20 @@ void WindowState::ToggleMaximized() {
 }
 
 void WindowState::ToggleFullscreen() {
-  // Window which cannot be maximized should not be fullscreened.
-  // It can, however, be restored if it was fullscreened.
   bool is_fullscreen = IsFullscreen();
-  if (!is_fullscreen && !CanMaximize())
-    return;
-  if (delegate_ && delegate_->ToggleFullscreen(this))
-    return;
   if (is_fullscreen) {
-    Restore();
+    if (delegate_ && delegate_->ExitFullscreen(this))
+      return;
+   Restore();
   } else {
-    window_->SetProperty(aura::client::kShowStateKey,
-                         ui::SHOW_STATE_FULLSCREEN);
+    // Windows which cannot be maximized should not be fullscreened.
+    if (CanMaximize()) {
+      if (delegate_ && delegate_->EnterImmersiveFullscreen(this))
+        return;
+
+      window_->SetProperty(aura::client::kShowStateKey,
+                           ui::SHOW_STATE_FULLSCREEN);
+    }
   }
 }