[VK] Remove unused WindowObserver events.

KeyboardController listens to WindowObserver events on the parent
container window. It updates the observer whenever the keyboard moves
to a different display by removing the observer on the old root window
and adding the observer on the new root window. See original patch
that added the code:
https://crrev.com/1008453002

We don't really need to do this as we already do that in Activate/
Deactivate keyboard.

Bug: 845780
Change-Id: Idc25d5beadbe1f2233e184fd1c189a3fde05aa50
Reviewed-on: https://chromium-review.googlesource.com/1113714
Commit-Queue: Darren Shen <shend@chromium.org>
Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570970}

ui/keyboard/keyboard_controller.cc

@@ -515,15 +515,8 @@ void KeyboardController::OnWindowHierarchyChanged(
 }
 
 void KeyboardController::OnWindowAddedToRootWindow(aura::Window* window) {
-  if (!window->GetRootWindow()->HasObserver(this))
-    window->GetRootWindow()->AddObserver(this);
-  AdjustKeyboardBounds();
-}
-
-void KeyboardController::OnWindowRemovingFromRootWindow(aura::Window* window,
-    aura::Window* new_root) {
-  if (window->GetRootWindow()->HasObserver(this))
-    window->GetRootWindow()->RemoveObserver(this);
+  container_behavior_->SetCanonicalBounds(GetContentsWindow(),
+                                          GetRootWindow()->bounds());
 }
 
 void KeyboardController::OnWindowBoundsChanged(
@@ -723,11 +716,6 @@ void KeyboardController::NotifyKeyboardConfigChanged() {
     observer.OnKeyboardConfigChanged();
 }
 
-void KeyboardController::AdjustKeyboardBounds() {
-  container_behavior_->SetCanonicalBounds(GetContentsWindow(),
-                                          GetRootWindow()->bounds());
-}
-
 void KeyboardController::CheckStateTransition(KeyboardControllerState prev,
                                               KeyboardControllerState next) {
   std::stringstream error_message;

ui/keyboard/keyboard_controller.h

@@ -271,8 +271,6 @@ class KEYBOARD_EXPORT KeyboardController
   // aura::WindowObserver overrides
   void OnWindowHierarchyChanged(const HierarchyChangeParams& params) override;
   void OnWindowAddedToRootWindow(aura::Window* window) override;
-  void OnWindowRemovingFromRootWindow(aura::Window* window,
-                                      aura::Window* new_root) override;
   void OnWindowBoundsChanged(aura::Window* window,
                              const gfx::Rect& old_bounds,
                              const gfx::Rect& new_bounds,
@@ -309,10 +307,6 @@ class KEYBOARD_EXPORT KeyboardController
 
   void NotifyKeyboardBoundsChangingAndEnsureCaretInWorkArea();
 
-  // Called when the keyboard mode is set or the keyboard is moved to another
-  // display.
-  void AdjustKeyboardBounds();
-
   // Notifies keyboard config change to the observers.
   // Only called from |UpdateKeyboardConfig| in keyboard_util.
   void NotifyKeyboardConfigChanged();