Adopt display::DisplayObserver::OnDisplayTabletStateChanged()

.... over chromeos::TabletState::Observer.

This CL is a follow up of crrev.com/c/2491517. It gets rid of
chromeos::TabletState::Observer class in favor of
display::DisplayObserver::OnDisplayTabletStateChanged().

The CL also removes the use of the `friend class` declaration in
chromeos::TabletState: ash::TabletModeController now sets the
tablet state through display::DisplayManager ->
display::DisplayObserver::OnDisplayTabletStateChanged().

Last, the CL deliberately did not got rid of chromeos::TabletState
class. Reason: TabletState can continue to be a central read-only
class for query the tablet state from any where in the source base.

BUG=1113900
R=jamescook@chromium.org

Change-Id: I532e8511c1173139937c36c5e4c282311ea17576
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2518128
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823963}

ash/wm/tablet_mode/tablet_mode_controller.cc

@@ -841,7 +841,8 @@ void TabletModeController::SetTabletModeEnabledInternal(bool should_enable) {
   DeleteScreenshot();
 
   if (should_enable) {
-    tablet_state_.SetState(display::TabletState::kEnteringTabletMode);
+    Shell::Get()->display_manager()->NotifyDisplayTabletStateChanged(
+        display::TabletState::kEnteringTabletMode);
 
     // Take a screenshot if there is a top window that will get animated.
     // TODO(sammiequon): Handle the case where the top window is not on the
@@ -871,7 +872,8 @@ void TabletModeController::SetTabletModeEnabledInternal(bool should_enable) {
       FinishInitTabletMode();
     }
   } else {
-    tablet_state_.SetState(display::TabletState::kExitingTabletMode);
+    Shell::Get()->display_manager()->NotifyDisplayTabletStateChanged(
+        display::TabletState::kExitingTabletMode);
 
     // We may have entered tablet mode, then tried to exit before the screenshot
     // was taken. In this case |tablet_mode_window_manager_| will be null.
@@ -887,7 +889,8 @@ void TabletModeController::SetTabletModeEnabledInternal(bool should_enable) {
 
     base::RecordAction(base::UserMetricsAction("Touchview_Disabled"));
     RecordTabletModeUsageInterval(TABLET_MODE_INTERVAL_ACTIVE);
-    tablet_state_.SetState(display::TabletState::kInClamshellMode);
+    Shell::Get()->display_manager()->NotifyDisplayTabletStateChanged(
+        display::TabletState::kInClamshellMode);
     for (auto& observer : tablet_mode_observers_)
       observer.OnTabletModeEnded();
     VLOG(1) << "Exit tablet mode.";
@@ -1140,7 +1143,8 @@ void TabletModeController::FinishInitTabletMode() {
 
   base::RecordAction(base::UserMetricsAction("Touchview_Enabled"));
   RecordTabletModeUsageInterval(TABLET_MODE_INTERVAL_INACTIVE);
-  tablet_state_.SetState(display::TabletState::kInTabletMode);
+  Shell::Get()->display_manager()->NotifyDisplayTabletStateChanged(
+      display::TabletState::kInTabletMode);
 
   for (auto& observer : tablet_mode_observers_)
     observer.OnTabletModeStarted();

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

@@ -36,6 +36,7 @@
 #include "chrome/browser/ui/web_applications/system_web_app_ui_utils.h"
 #include "chromeos/constants/chromeos_features.h"
 #include "chromeos/ui/base/chromeos_ui_constants.h"
+#include "chromeos/ui/base/tablet_state.h"
 #include "chromeos/ui/base/window_properties.h"
 #include "chromeos/ui/base/window_state_type.h"
 #include "chromeos/ui/frame/caption_buttons/frame_caption_button_container_view.h"
@@ -47,6 +48,7 @@
 #include "ui/aura/env.h"
 #include "ui/base/hit_test.h"
 #include "ui/base/layout.h"
+#include "ui/display/screen.h"
 #include "ui/events/gestures/gesture_recognizer.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/geometry/rect.h"
@@ -94,7 +96,7 @@ BrowserNonClientFrameViewAsh::BrowserNonClientFrameViewAsh(
 }
 
 BrowserNonClientFrameViewAsh::~BrowserNonClientFrameViewAsh() {
-  chromeos::TabletState::Get()->RemoveObserver(this);
+  display::Screen::GetScreen()->RemoveObserver(this);
 
   ImmersiveModeController* immersive_controller =
       browser_view()->immersive_mode_controller();
@@ -133,7 +135,7 @@ void BrowserNonClientFrameViewAsh::Init() {
   if (browser->profile()->IsOffTheRecord())
     window->SetProperty(ash::kBlockedForAssistantSnapshotKey, true);
 
-  chromeos::TabletState::Get()->AddObserver(this);
+  display::Screen::GetScreen()->AddObserver(this);
 
   if (frame()->ShouldDrawFrameHeader())
     frame_header_ = CreateFrameHeader();
@@ -414,7 +416,7 @@ gfx::ImageSkia BrowserNonClientFrameViewAsh::GetFrameHeaderOverlayImage(
                                      : BrowserFrameActiveState::kInactive);
 }
 
-void BrowserNonClientFrameViewAsh::OnTabletStateChanged(
+void BrowserNonClientFrameViewAsh::OnDisplayTabletStateChanged(
     display::TabletState state) {
   switch (state) {
     case display::TabletState::kInTabletMode:

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

@@ -15,9 +15,9 @@
 #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"
+#include "ui/display/display_observer.h"
 #include "ui/display/tablet_state.h"
 
 namespace {
@@ -35,7 +35,7 @@ class FrameCaptionButtonContainerView;
 class BrowserNonClientFrameViewAsh
     : public BrowserNonClientFrameView,
       public BrowserFrameHeaderAsh::AppearanceProvider,
-      public chromeos::TabletState::Observer,
+      public display::DisplayObserver,
       public TabIconViewModel,
       public aura::WindowObserver,
       public ImmersiveModeController::Observer {
@@ -82,8 +82,8 @@ class BrowserNonClientFrameViewAsh
   int GetFrameHeaderImageYInset() override;
   gfx::ImageSkia GetFrameHeaderOverlayImage(bool active) override;
 
-  // chromeos::TabletState::Observer:
-  void OnTabletStateChanged(display::TabletState state) override;
+  // display::DisplayObserver:
+  void OnDisplayTabletStateChanged(display::TabletState state) override;
 
   void OnTabletModeToggled(bool enabled);
 

chromeos/ui/base/tablet_state.cc

@@ -29,28 +29,13 @@ TabletState::~TabletState() {
   display::Screen::GetScreen()->RemoveObserver(this);
 }
 
-void TabletState::AddObserver(Observer* observer) {
-  observers_.AddObserver(observer);
-}
-
-void TabletState::RemoveObserver(Observer* observer) {
-  observers_.RemoveObserver(observer);
-}
-
 bool TabletState::InTabletMode() const {
   return state_ == display::TabletState::kInTabletMode ||
          state_ == display::TabletState::kEnteringTabletMode;
 }
 
-void TabletState::SetState(display::TabletState state) {
-  state_ = state;
-
-  for (auto& observer : observers_)
-    observer.OnTabletStateChanged(state_);
-}
-
 void TabletState::OnDisplayTabletStateChanged(display::TabletState state) {
-  SetState(state);
+  state_ = state;
 }
 
 }  // namespace chromeos

chromeos/ui/base/tablet_state.h

@@ -6,42 +6,26 @@
 #define CHROMEOS_UI_BASE_TABLET_STATE_H_
 
 #include "base/component_export.h"
-#include "base/observer_list.h"
 #include "ui/display/display_observer.h"
 #include "ui/display/tablet_state.h"
 
-namespace ash {
-class TabletModeController;
-}
-
 namespace chromeos {
 
 // Class is a singleton and holds the tablet mode state.
 //
-// The idea is that only the creator of this class in Ash or Lacros/Ozone code
-// is able to set the state.
+// TODO(crbug.com/1113900): Move the logic to display::Screen::GetTabletState()
+// and implement it for Ash and Ozone child classes.
 class COMPONENT_EXPORT(CHROMEOS_UI_BASE) TabletState
     : public display::DisplayObserver {
  public:
   // Returns the singleton instance.
   static TabletState* Get();
 
-  class COMPONENT_EXPORT(CHROMEOS_UI_BASE) Observer {
-   public:
-    virtual void OnTabletStateChanged(display::TabletState state) = 0;
-
-   protected:
-    virtual ~Observer() = default;
-  };
-
   TabletState();
   TabletState(const TabletState&) = delete;
   TabletState& operator=(const TabletState&) = delete;
   ~TabletState() override;
 
-  void AddObserver(Observer* observer);
-  void RemoveObserver(Observer* observer);
-
   // Returns true if the system is in tablet mode.
   bool InTabletMode() const;
 
@@ -51,14 +35,6 @@ class COMPONENT_EXPORT(CHROMEOS_UI_BASE) TabletState
   void OnDisplayTabletStateChanged(display::TabletState state) override;
 
  private:
-  // The friend class declaration here is used to control classes that can set
-  // the tablet state.
-  friend class ash::TabletModeController;
-
-  void SetState(display::TabletState state);
-
-  base::ObserverList<Observer>::Unchecked observers_;
-
   display::TabletState state_ = display::TabletState::kInClamshellMode;
 };
 

ui/display/manager/display_manager.cc

@@ -36,6 +36,7 @@
 #include "ui/display/manager/display_util.h"
 #include "ui/display/manager/managed_display_info.h"
 #include "ui/display/screen.h"
+#include "ui/display/tablet_state.h"
 #include "ui/display/types/display_snapshot.h"
 #include "ui/gfx/font_render_params.h"
 #include "ui/gfx/geometry/rect.h"
@@ -2192,6 +2193,12 @@ void DisplayManager::NotifyDisplayRemoved(const Display& display) {
     observer.OnDisplayRemoved(display);
 }
 
+void DisplayManager::NotifyDisplayTabletStateChanged(
+    const TabletState& tablet_state) {
+  for (auto& observer : observers_)
+    observer.OnDisplayTabletStateChanged(tablet_state);
+}
+
 void DisplayManager::AddObserver(DisplayObserver* observer) {
   observers_.AddObserver(observer);
 }

ui/display/manager/display_manager.h

@@ -50,6 +50,7 @@ class DisplayLayoutStore;
 class DisplayObserver;
 class NativeDisplayDelegate;
 class Screen;
+enum class TabletState;
 
 namespace test {
 class DisplayManagerTestApi;
@@ -492,6 +493,7 @@ class DISPLAY_MANAGER_EXPORT DisplayManager
   void NotifyMetricsChanged(const Display& display, uint32_t metrics);
   void NotifyDisplayAdded(const Display& display);
   void NotifyDisplayRemoved(const Display& display);
+  void NotifyDisplayTabletStateChanged(const TabletState& tablet_state);
 
   // Delegated from the Screen implementation.
   void AddObserver(DisplayObserver* observer);