Introduce WindowStateDelegate::ToggleFullscreen

ash/accelerators/accelerator_commands.h

Index: ash/accelerators/accelerator_commands.h
diff --git a/ash/accelerators/accelerator_commands.h b/ash/accelerators/accelerator_commands.h
index 36006e7ebede569ef092457fd92d14bdf1fb86a0..f199068261954163dd6573e84f91293a17ea2399 100644
--- a/ash/accelerators/accelerator_commands.h
+++ b/ash/accelerators/accelerator_commands.h
@@ -21,6 +21,11 @@ ASH_EXPORT bool ToggleMinimized();
 // fullscreen mode.
 ASH_EXPORT void ToggleMaximized();
 
+// Toggles the fullscreen state. If the window is already in
+// maximized, it exits maximized mode. The behavior can be overridden

[pkotwicz, 2013/10/29 00:46:01]

"If the window is already in maximized, it exits maximized mode." is not true

+// by |WindowStateDelegate::ToggleFullscreen()|.
+ASH_EXPORT void ToggleFullscreen();
+
 }  // namespace accelerators
 }  // namespace ash