CrOS Shelf: Minor widget activation simplification

In |ShelfWidget|, override |OnNativeWidgetActivationChanged| instead of
|OnWidgetActivationChanged|. This achieves the same purpose, is more
consistent with what |StatusAreaWidget| does, and avoids the need to
add/remove widget observers.

Note that this doesn't directly fix the linked bug but is a step in the
right direction. No behavior change is expected from this change.

Bug: 956080
Change-Id: Id4002b30197a5d6a97baccaaf1a912db39c45e9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1643413Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Manu Cornet <manucornet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666027}

ash/shelf/shelf_widget.cc

@@ -368,8 +368,6 @@ ShelfWidget::ShelfWidget(aura::Window* shelf_container, Shelf* shelf)
       shelf_layout_manager_->GetShelfBackgroundType(),
       AnimationChangeType::IMMEDIATE);
 
-  views::Widget::AddObserver(this);
-
   background_animator_.AddObserver(delegate_view_);
   shelf_->AddObserver(this);
 
@@ -414,7 +412,6 @@ void ShelfWidget::Shutdown() {
   // Don't need to observe focus/activation during shutdown.
   Shell::Get()->focus_cycler()->RemoveWidget(this);
   SetFocusCycler(nullptr);
-  RemoveObserver(this);
 }
 
 void ShelfWidget::CreateStatusAreaWidget(aura::Window* status_container) {
@@ -522,20 +519,22 @@ void ShelfWidget::FocusFirstOrLastFocusableChild(bool last) {
   to_focus->GetFocusManager()->SetFocusedView(to_focus);
 }
 
-void ShelfWidget::OnWidgetActivationChanged(views::Widget* widget,
-                                            bool active) {
+bool ShelfWidget::OnNativeWidgetActivationChanged(bool active) {
+  if (!Widget::OnNativeWidgetActivationChanged(active))
+    return false;
   if (active) {
     // Do not focus the default element if the widget activation came from the
     // another widget's focus cycling. The setter of
     // |activated_from_other_widget_| should handle focusing the correct view.
     if (activated_from_other_widget_) {
       activated_from_other_widget_ = false;
-      return;
+      return true;
     }
     delegate_view_->SetPaneFocusAndFocusDefault();
   } else {
     delegate_view_->GetFocusManager()->ClearFocus();
   }
+  return true;
 }
 
 void ShelfWidget::WillDeleteShelfLayoutManager() {

ash/shelf/shelf_widget.h

@@ -16,7 +16,6 @@
 #include "ash/shelf/shelf_observer.h"
 #include "base/macros.h"
 #include "ui/views/widget/widget.h"
-#include "ui/views/widget/widget_observer.h"
 
 namespace app_list {
 class ApplicationDragAndDropHost;
@@ -37,7 +36,6 @@ class StatusAreaWidget;
 // the status area widget. There is one ShelfWidget per display. It is created
 // early during RootWindowController initialization.
 class ASH_EXPORT ShelfWidget : public views::Widget,
-                               public views::WidgetObserver,
                                public ShelfLayoutManagerObserver,
                                public ShelfObserver,
                                public SessionObserver,
@@ -106,10 +104,12 @@ class ASH_EXPORT ShelfWidget : public views::Widget,
   // and focuses it.
   void FocusFirstOrLastFocusableChild(bool last);
 
-  // Overridden from views::WidgetObserver:
-  void OnWidgetActivationChanged(views::Widget* widget, bool active) override;
+  // views::Widget:
+  void OnMouseEvent(ui::MouseEvent* event) override;
+  void OnGestureEvent(ui::GestureEvent* event) override;
+  bool OnNativeWidgetActivationChanged(bool active) override;
 
-  // ShelfLayoutManagerObserver overrides:
+  // ShelfLayoutManagerObserver:
   void WillDeleteShelfLayoutManager() override;
 
   // ShelfObserver:
@@ -148,10 +148,6 @@ class ASH_EXPORT ShelfWidget : public views::Widget,
   // Shows shelf widget if IsVisible() returns false.
   void ShowIfHidden();
 
-  // views::Widget:
-  void OnMouseEvent(ui::MouseEvent* event) override;
-  void OnGestureEvent(ui::GestureEvent* event) override;
-
   Shelf* shelf_;
 
   ShelfBackgroundAnimator background_animator_;