Reland r786979, part 4: remove ButtonObserver.

The original CL was landed in one piece and reverted due to apparent
perf regressions.  Reland in sections to try and determine more
precisely whether there is any perf impact.

This CL removes ButtonObserver entirely, which should be unused.

If this causes perf regressions... something about cache alignment??

Bug: none
Change-Id: If9c0f40d50c9122d5830067eab0b2e2d63d00b2a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2346535
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Allen Bauer <kylixrd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796638}

ui/views/BUILD.gn

@@ -109,7 +109,6 @@ component("views") {
     "controls/button/button.h",
     "controls/button/button_controller.h",
     "controls/button/button_controller_delegate.h",
-    "controls/button/button_observer.h",
     "controls/button/checkbox.h",
     "controls/button/image_button.h",
     "controls/button/image_button_factory.h",

ui/views/controls/button/button.cc

@@ -20,7 +20,6 @@
 #include "ui/views/animation/ink_drop_impl.h"
 #include "ui/views/controls/button/button_controller.h"
 #include "ui/views/controls/button/button_controller_delegate.h"
-#include "ui/views/controls/button/button_observer.h"
 #include "ui/views/controls/button/checkbox.h"
 #include "ui/views/controls/button/image_button.h"
 #include "ui/views/controls/button/label_button.h"
@@ -238,16 +237,6 @@ void Button::SetHighlighted(bool bubble_visible) {
   AnimateInkDrop(bubble_visible ? views::InkDropState::ACTIVATED
                                 : views::InkDropState::DEACTIVATED,
                  nullptr);
-  for (ButtonObserver& observer : button_observers_)
-    observer.OnHighlightChanged(this, bubble_visible);
-}
-
-void Button::AddButtonObserver(ButtonObserver* observer) {
-  button_observers_.AddObserver(observer);
-}
-
-void Button::RemoveButtonObserver(ButtonObserver* observer) {
-  button_observers_.RemoveObserver(observer);
 }
 
 PropertyChangedSubscription Button::AddStateChangedCallback(
@@ -533,10 +522,7 @@ void Button::OnClickCanceled(const ui::Event& event) {
 
 void Button::OnSetTooltipText(const base::string16& tooltip_text) {}
 
-void Button::StateChanged(ButtonState old_state) {
-  for (ButtonObserver& observer : button_observers_)
-    observer.OnStateChanged(this, old_state);
-}
+void Button::StateChanged(ButtonState old_state) {}
 
 bool Button::IsTriggerableEvent(const ui::Event& event) {
   return button_controller_->IsTriggerableEvent(event);

ui/views/controls/button/button.h

@@ -27,7 +27,6 @@ class ButtonTestApi;
 
 class Button;
 class ButtonController;
-class ButtonObserver;
 class Event;
 
 // An interface implemented by an object to let it know that a button was
@@ -178,8 +177,6 @@ class VIEWS_EXPORT Button : public InkDropHostView,
   // Highlights the ink drop for the button.
   void SetHighlighted(bool bubble_visible);
 
-  void AddButtonObserver(ButtonObserver* observer);
-  void RemoveButtonObserver(ButtonObserver* observer);
   PropertyChangedSubscription AddStateChangedCallback(
       PropertyChangedCallback callback);
 
@@ -357,8 +354,6 @@ class VIEWS_EXPORT Button : public InkDropHostView,
       AddEnabledChangedCallback(base::BindRepeating(&Button::OnEnabledChanged,
                                                     base::Unretained(this)))};
 
-  base::ObserverList<ButtonObserver> button_observers_;
-
   DISALLOW_COPY_AND_ASSIGN(Button);
 };
 

ui/views/controls/button/button_observer.h

-// Copyright 2019 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef UI_VIEWS_CONTROLS_BUTTON_BUTTON_OBSERVER_H_
-#define UI_VIEWS_CONTROLS_BUTTON_BUTTON_OBSERVER_H_
-
-#include "base/observer_list_types.h"
-#include "ui/views/controls/button/button.h"
-#include "ui/views/views_export.h"
-
-namespace views {
-
-class VIEWS_EXPORT ButtonObserver : public base::CheckedObserver {
- public:
-  virtual void OnHighlightChanged(views::Button* observed_button,
-                                  bool highlighted) {}
-
-  virtual void OnStateChanged(views::Button* observed_button,
-                              views::Button::ButtonState old_state) {}
-
- protected:
-  ~ButtonObserver() override = default;
-};
-
-}  // namespace views
-
-#endif  // UI_VIEWS_CONTROLS_BUTTON_BUTTON_OBSERVER_H_