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

This is identical to the original CL (https://crrev.com/c/2462560).
The fix happened on the predecessor CL (https://crrev.com/c/2466739).

Original change's description:

> 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=jamescook@chromium.org, sky@chromium.org
>
> 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

Change-Id: Ic9cc488266a42ca4efc40fdfe4edbf7e00c8f93c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2468496
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Reviewed-by: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#816712}

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

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

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

@@ -7,7 +7,6 @@
 
 #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"
@@ -16,6 +15,7 @@
 #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 ash::TabletModeObserver,
+      public chromeos::TabletState::Observer,
       public TabIconViewModel,
       public aura::WindowObserver,
       public ImmersiveModeController::Observer {
@@ -81,9 +81,8 @@ class BrowserNonClientFrameViewAsh
   int GetFrameHeaderImageYInset() override;
   gfx::ImageSkia GetFrameHeaderOverlayImage(bool active) override;
 
-  // ash::TabletModeObserver:
-  void OnTabletModeStarted() override;
-  void OnTabletModeEnded() override;
+  // chromeos::TabletState::Observer:
+  void OnTabletStateChanged(chromeos::TabletState::State) override;
 
   void OnTabletModeToggled(bool enabled);
 

chromeos/ui/base/tablet_state.cc

@@ -26,9 +26,24 @@ 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

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