Revert of Hook up views/widgets to AshDevToolsDOMAgent

ash/common/devtools/ash_devtools_dom_agent.h

Index: ash/common/devtools/ash_devtools_dom_agent.h
diff --git a/ash/common/devtools/ash_devtools_dom_agent.h b/ash/common/devtools/ash_devtools_dom_agent.h
index de4d23b7b6c9085f21fb94279146502f88438cc5..b79f606ac7d317aff8d92b3d7a0ca657c41101a5 100644
--- a/ash/common/devtools/ash_devtools_dom_agent.h
+++ b/ash/common/devtools/ash_devtools_dom_agent.h
@@ -11,9 +11,7 @@
 #include "components/ui_devtools/DOM.h"
 #include "components/ui_devtools/devtools_base_agent.h"
 #include "ui/views/view.h"
-#include "ui/views/view_observer.h"
 #include "ui/views/widget/widget.h"
-#include "ui/views/widget/widget_removals_observer.h"
 
 namespace ash {
 namespace devtools {
@@ -21,9 +19,7 @@
 class ASH_EXPORT AshDevToolsDOMAgent
     : public NON_EXPORTED_BASE(ui::devtools::UiDevToolsBaseAgent<
                                ui::devtools::protocol::DOM::Metainfo>),
-      public WmWindowObserver,
-      public views::WidgetRemovalsObserver,
-      public views::ViewObserver {
+      public WmWindowObserver {
  public:
   explicit AshDevToolsDOMAgent(ash::WmShell* shell);
   ~AshDevToolsDOMAgent() override;
@@ -39,14 +35,6 @@
   void OnWindowTreeChanged(WmWindow* window,
                            const TreeChangeParams& params) override;
   void OnWindowStackingChanged(WmWindow* window) override;
-
-  // views::WidgetRemovalsObserver
-  void OnWillRemoveView(views::Widget* widget, views::View* view) override;
-
-  // views::ViewObserver
-  void OnChildViewRemoved(views::View* view, views::View* parent) override;
-  void OnChildViewAdded(views::View* view) override;
-  void OnChildViewReordered(views::View*) override;
 
   WmWindow* GetWindowFromNodeId(int nodeId);
   views::Widget* GetWidgetFromNodeId(int nodeId);
@@ -73,12 +61,9 @@
   void RemoveWindowTree(WmWindow* window, bool remove_observer);
   void RemoveWindowNode(WmWindow* window, bool remove_observer);
 
-  // Don't need AddWidgetTree because |widget| will always be inside a window,
-  // so when windows are created, their widget nodes are created as well.
   void RemoveWidgetTree(views::Widget* widget, bool remove_observer);
   void RemoveWidgetNode(views::Widget* widget, bool remove_observer);
 
-  void AddViewTree(views::View* view);
   void RemoveViewTree(views::View* view,
                       views::View* parent,
                       bool remove_observer);
@@ -86,7 +71,7 @@
                       views::View* parent,
                       bool remove_observer);
 
-  void RemoveObservers();
+  void RemoveObserverFromAllWindows();
   void Reset();
 
   ash::WmShell* shell_;