Add ViewObserver to View for view updates

ui/views/view.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_VIEWS_VIEW_H_
 #define UI_VIEWS_VIEW_H_
 
 #include <stddef.h>
 
 #include <algorithm>
@@ skipping 56 matching lines @@
 
 class Background;
 class Border;
 class ContextMenuController;
 class DragController;
 class FocusManager;
 class FocusTraversable;
 class LayoutManager;
 class NativeViewAccessibility;
 class ScrollView;
+class ViewObserver;
 class Widget;
 class WordLookupClient;
 
 namespace internal {
 class PreEventDispatchHandler;
 class PostEventDispatchHandler;
 class RootView;
 }
 
 /////////////////////////////////////////////////////////////////////////////
@@ skipping 906 matching lines @@
   // to scroll. ScrollView interprets a return value of 0 (or negative)
   // to scroll by a default amount.
   //
   // See VariableRowHeightScrollHelper and FixedRowHeightScrollHelper for
   // implementations of common cases.
   virtual int GetPageScrollIncrement(ScrollView* scroll_view,
                                      bool is_horizontal, bool is_positive);
   virtual int GetLineScrollIncrement(ScrollView* scroll_view,
                                      bool is_horizontal, bool is_positive);
 
+  void AddObserver(ViewObserver* observer);
+  void RemoveObserver(ViewObserver* observer);
+  bool HasObserver(const ViewObserver* observer) const;
+
  protected:
   // Used to track a drag. RootView passes this into
   // ProcessMousePressed/Dragged.
   struct DragInfo {
     // Sets possible_drag to false and start_x/y to 0. This is invoked by
     // RootView prior to invoke ProcessMousePressed.
     void Reset();
 
     // Sets possible_drag to true and start_pt to the specified point.
     // This is invoked by the target view if it detects the press may generate
@@ skipping 415 matching lines @@
 
   // Starts a drag and drop operation originating from this view. This invokes
   // WriteDragData to write the data and GetDragOperations to determine the
   // supported drag operations. When done, OnDragDone is invoked. |press_pt| is
   // in the view's coordinate system.
   // Returns true if a drag was started.
   bool DoDrag(const ui::LocatedEvent& event,
               const gfx::Point& press_pt,
               ui::DragDropTypes::DragEventSource source);
 
+  // Called after the |child| has been added to its parent. Called on observers
+  // listening to |child|'s parent.
+  void NotifyChildViewAdded(View* child);

[sky, 2016/11/22 04:40:48]

You only call these functions from one place, inline the implementation there.

[Sarmad Hashmi, 2016/11/22 04:47:00]

Moved the implementations to where they were called from instead.

+  // Called after the |child| has been removed from its |parent|. Called on
+  // observers listening to |parent|.
+  void NotifyChildViewRemoved(View* child);
+
   //////////////////////////////////////////////////////////////////////////////
 
   // Creation and lifetime -----------------------------------------------------
 
   // False if this View is owned by its parent - i.e. it will be deleted by its
   // parent during its parents destruction. False is the default.
   bool owned_by_client_;
 
   // Attributes ----------------------------------------------------------------
 
@@ skipping 120 matching lines @@
   // Input  --------------------------------------------------------------------
 
   std::unique_ptr<ViewTargeter> targeter_;
 
   // Accessibility -------------------------------------------------------------
 
   // Belongs to this view, but it's reference-counted on some platforms
   // so we can't use a scoped_ptr. It's dereferenced in the destructor.
   NativeViewAccessibility* native_view_accessibility_;
 
+  // Observers -------------------------------------------------------------
+
+  base::ObserverList<ViewObserver> observers_;
+
   DISALLOW_COPY_AND_ASSIGN(View);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_VIEW_H_