Add virtualKeyboardPrivate.onKeyboardClosed API.

ui/keyboard/keyboard_controller.cc

Index: ui/keyboard/keyboard_controller.cc
diff --git a/ui/keyboard/keyboard_controller.cc b/ui/keyboard/keyboard_controller.cc
index 71b55b02c233ceadb1d8a5979418674efbf0e06b..ff71e8145ccc3ea5d07e93b1d40bb1c1c3c88d10 100644
--- a/ui/keyboard/keyboard_controller.cc
+++ b/ui/keyboard/keyboard_controller.cc
@@ -185,6 +185,8 @@ KeyboardController::~KeyboardController() {
     if (container_->GetRootWindow())
       container_->GetRootWindow()->RemoveObserver(this);
     container_->RemoveObserver(this);
+    FOR_EACH_OBSERVER(KeyboardControllerObserver, observer_list_,

[sky, 2016/07/06 16:03:00]

How come you're only calling OnKeyboardDestroyed() if there is a container_?
Also, why aren't you calling notifiers as the last thing in this function?

[Azure Wei, 2016/07/08 06:35:24]

Want to make sure the container_ has been created (VK has ever been shown) to
trigger the event. While, it should not happen that KeyboardController is
created with no container_.
Moved it to the last of the function.

+                      OnKeyboardDestroyed());
   }
   if (input_method_)
     input_method_->RemoveObserver(this);