Revert "Add TabletState::Observer and adopt in BrowserNonClientFrameViewAsh"

This reverts commit 2ad3f0c5.

Reason for revert: CL:https://crrev.com/c/2458768 is likely the cause that create ash_unittests and browser_tests failures in linux-chromeos-dbg build starting from https://ci.chromium.org/p/chromium/builders/ci/linux-chromeos-dbg/20815. The failed tests are FrameSizeButtonTest, ImmersiveModeBrowserViewTestNoWebUiTabStrip and ImmersiveModeBrowserViewTest. I'm not 100% sure this CL is depend on the culprit, but it is linked from that CL, so I reverted this just in case. 

Original change's description:
> Add TabletState::Observer and adopt in BrowserNonClientFrameViewAsh
>
> This replaces the use of ash::TabletMode and ash::TabletModeObserver in
> BrowserNonClientFrameViewAsh.
>
> This corresponds to phase 2.6 on the design document [1].
>
> Covered by existing tests, eg
>
> BrowserNonClientFrameViewAshTest.BrowserHeaderVisibilityInTabletModeTest
> HomeLauncherBrowserNonClientFrameViewAshTest.TabletModeBrowserCaptionButtonVisibility
>
> [1] https://docs.google.com/document/d/1xHwcHrAiEaWuA4usGEqKZ9zm1H8SGk3WkS-Jf2Q_los/
>
> BUG=1113900
> R=​sky@chromium.org
>
> Change-Id: I6a21ca44538e52a2712bbb936221aa24063daa36
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2462560
> Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
> Reviewed-by: James Cook <jamescook@chromium.org>
> Reviewed-by: Scott Violet <sky@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#816316}

TBR=jamescook@chromium.org,sky@chromium.org,tonikitoo@igalia.com

Change-Id: I8f8ad38e07c26eee09fec0efc6ca3cbf882a2719
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1113900
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2466014Reviewed-by: Maggie Cai <mxcai@chromium.org>
Commit-Queue: Maggie Cai <mxcai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816384}

chrome/browser/ui/views/frame/browser_non_client_frame_view_ash.cc

@@ -9,6 +9,7 @@
 #include "ash/public/cpp/app_types.h"
 #include "ash/public/cpp/default_frame_header.h"
 #include "ash/public/cpp/frame_utils.h"
+#include "ash/public/cpp/tablet_mode.h"
 #include "ash/public/cpp/window_properties.h"
 #include "ash/wm/window_util.h"
 #include "base/metrics/user_metrics.h"
@@ -94,7 +95,7 @@ BrowserNonClientFrameViewAsh::BrowserNonClientFrameViewAsh(
 }
 
 BrowserNonClientFrameViewAsh::~BrowserNonClientFrameViewAsh() {
-  chromeos::TabletState::Get()->RemoveObserver(this);
+  ash::TabletMode::Get()->RemoveObserver(this);
 
   ImmersiveModeController* immersive_controller =
       browser_view()->immersive_mode_controller();
@@ -133,7 +134,7 @@ void BrowserNonClientFrameViewAsh::Init() {
   if (browser->profile()->IsOffTheRecord())
     window->SetProperty(ash::kBlockedForAssistantSnapshotKey, true);
 
-  chromeos::TabletState::Get()->AddObserver(this);
+  ash::TabletMode::Get()->AddObserver(this);
 
   if (frame()->ShouldDrawFrameHeader())
     frame_header_ = CreateFrameHeader();
@@ -414,19 +415,12 @@ gfx::ImageSkia BrowserNonClientFrameViewAsh::GetFrameHeaderOverlayImage(
                                      : BrowserFrameActiveState::kInactive);
 }
 
-void BrowserNonClientFrameViewAsh::OnTabletStateChanged(
-    chromeos::TabletState::State state) {
-  switch (state) {
-    case chromeos::TabletState::State::kInTabletMode:
-      OnTabletModeToggled(true);
-      return;
-    case chromeos::TabletState::State::kInClamshellMode:
-      OnTabletModeToggled(false);
-      return;
-    case chromeos::TabletState::State::kEnteringTabletMode:
-    case chromeos::TabletState::State::kExitingTabletMode:
-      break;
-  }
+void BrowserNonClientFrameViewAsh::OnTabletModeStarted() {
+  OnTabletModeToggled(true);
+}
+
+void BrowserNonClientFrameViewAsh::OnTabletModeEnded() {
+  OnTabletModeToggled(false);
 }
 
 void BrowserNonClientFrameViewAsh::OnTabletModeToggled(bool enabled) {
@@ -565,7 +559,7 @@ bool BrowserNonClientFrameViewAsh::ShouldShowCaptionButtons() const {
 bool BrowserNonClientFrameViewAsh::ShouldShowCaptionButtonsWhenNotInOverview()
     const {
   return UsePackagedAppHeaderStyle(browser_view()->browser()) ||
-         !chromeos::TabletState::Get()->InTabletMode();
+         !ash::TabletMode::Get()->InTabletMode();
 }
 
 int BrowserNonClientFrameViewAsh::GetToolbarLeftInset() const {

chrome/browser/ui/views/frame/browser_non_client_frame_view_ash.h

@@ -7,6 +7,7 @@
 
 #include <memory>
 
+#include "ash/public/cpp/tablet_mode_observer.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
@@ -15,7 +16,6 @@
 #include "chrome/browser/ui/views/frame/browser_non_client_frame_view.h"
 #include "chrome/browser/ui/views/frame/immersive_mode_controller.h"
 #include "chrome/browser/ui/views/tab_icon_view_model.h"
-#include "chromeos/ui/base/tablet_state.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_observer.h"
 
@@ -34,7 +34,7 @@ class FrameCaptionButtonContainerView;
 class BrowserNonClientFrameViewAsh
     : public BrowserNonClientFrameView,
       public BrowserFrameHeaderAsh::AppearanceProvider,
-      public chromeos::TabletState::Observer,
+      public ash::TabletModeObserver,
       public TabIconViewModel,
       public aura::WindowObserver,
       public ImmersiveModeController::Observer {
@@ -81,8 +81,9 @@ class BrowserNonClientFrameViewAsh
   int GetFrameHeaderImageYInset() override;
   gfx::ImageSkia GetFrameHeaderOverlayImage(bool active) override;
 
-  // chromeos::TabletState::Observer:
-  void OnTabletStateChanged(chromeos::TabletState::State) override;
+  // ash::TabletModeObserver:
+  void OnTabletModeStarted() override;
+  void OnTabletModeEnded() override;
 
   void OnTabletModeToggled(bool enabled);
 

chromeos/ui/base/tablet_state.cc

@@ -26,24 +26,9 @@ TabletState::~TabletState() {
   g_instance = nullptr;
 }
 
-void TabletState::AddObserver(Observer* observer) {
-  observers_.AddObserver(observer);
-}
-
-void TabletState::RemoveObserver(Observer* observer) {
-  observers_.RemoveObserver(observer);
-}
-
 bool TabletState::InTabletMode() const {
   return state_ == TabletState::kInTabletMode ||
          state_ == TabletState::kEnteringTabletMode;
 }
 
-void TabletState::SetState(State state) {
-  state_ = state;
-
-  for (auto& observer : observers_)
-    observer.OnTabletStateChanged(state_);
-}
-
 }  // namespace chromeos

chromeos/ui/base/tablet_state.h

@@ -6,7 +6,6 @@
 #define CHROMEOS_UI_BASE_TABLET_STATE_H_
 
 #include "base/component_export.h"
-#include "base/observer_list.h"
 
 namespace ash {
 class TabletModeController;
@@ -32,21 +31,12 @@ class COMPONENT_EXPORT(CHROMEOS_UI_BASE) TabletState {
     kExitingTabletMode,
   };
 
-  class COMPONENT_EXPORT(CHROMEOS_UI_BASE) Observer {
-   public:
-    virtual void OnTabletStateChanged(State state) = 0;
-
-   protected:
-    virtual ~Observer() = default;
-  };
-
   TabletState();
   TabletState(const TabletState&) = delete;
   TabletState& operator=(const TabletState&) = delete;
   ~TabletState();
 
-  void AddObserver(Observer* observer);
-  void RemoveObserver(Observer* observer);
+  // TODO(http://crbug.com/1113900): Introduce Add|RemoveObserver support.
 
   // Returns true if the system is in tablet mode.
   bool InTabletMode() const;
@@ -58,9 +48,7 @@ class COMPONENT_EXPORT(CHROMEOS_UI_BASE) TabletState {
   // the tablet state.
   friend class ash::TabletModeController;
 
-  void SetState(State state);
-
-  base::ObserverList<Observer>::Unchecked observers_;
+  void SetState(State state) { state_ = state; }
 
   State state_ = State::kInClamshellMode;
 };

chromeos/ui/frame/caption_buttons/frame_back_button.h

@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef CHROMEOS_UI_FRAME_CAPTION_BUTTONS_FRAME_BACK_BUTTON_H_
-#define CHROMEOS_UI_FRAME_CAPTION_BUTTONS_FRAME_BACK_BUTTON_H_
+#ifndef ASH_PUBLIC_CPP_CAPTION_BUTTONS_FRAME_BACK_BUTTON_H_
+#define ASH_PUBLIC_CPP_CAPTION_BUTTONS_FRAME_BACK_BUTTON_H_
 
 #include "base/component_export.h"
 #include "ui/views/window/frame_caption_button.h"
@@ -28,4 +28,4 @@ class COMPONENT_EXPORT(CHROMEOS_UI_FRAME) FrameBackButton
 
 }  // namespace chromeos
 
-#endif  //  CHROMEOS_UI_FRAME_CAPTION_BUTTONS_FRAME_BACK_BUTTON_H_
+#endif  //  ASH_PUBLIC_CPP_CAPTION_BUTTONS_FRAME_BACK_BUTTON_H_