Introduce WindowStateDelegate::ToggleFullscreen

ash/accelerators/accelerator_commands.cc

Index: ash/accelerators/accelerator_commands.cc
diff --git a/ash/accelerators/accelerator_commands.cc b/ash/accelerators/accelerator_commands.cc
index 73f1b1a54387283c54298bb379c5143e60476bf4..003562e2b5d562a68db79a9913ea6d105711a5a2 100644
--- a/ash/accelerators/accelerator_commands.cc
+++ b/ash/accelerators/accelerator_commands.cc
@@ -37,10 +37,16 @@ void ToggleMaximized() {
     return;
   // Get out of fullscreen when in fullscreen mode.
   if (window_state->IsFullscreen())
-    Shell::GetInstance()->delegate()->ToggleFullscreen();
+    ToggleFullscreen();
   else
     window_state->ToggleMaximized();
 }
 
+void ToggleFullscreen() {
+  wm::WindowState* window_state = wm::GetActiveWindowState();
+  if (window_state)
+    window_state->ToggleFullscreen();
+}
+
 }  // namespace accelerators
 }  // namespace ash