Improve doc of ViewObserver and clarify arguments

ui/views/view.cc

 // 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.
 
 #define _USE_MATH_DEFINES // For VC++ to get M_PI. This has to be first.
 
 #include "ui/views/view.h"
 
 #include <algorithm>
 #include <cmath>
@@ skipping 234 matching lines @@
     RegisterChildrenForVisibleBoundsNotification(view);
 
     if (view->visible())
       view->SchedulePaint();
   }
 
   if (layout_manager_.get())
     layout_manager_->ViewAdded(this, view);
 
   for (ViewObserver& observer : observers_)
-    observer.OnChildViewAdded(view);
+    observer.OnChildViewAdded(this, view);
 }
 
 void View::ReorderChildView(View* view, int index) {
   DCHECK_EQ(view->parent_, this);
   if (index < 0)
     index = child_count() - 1;
   else if (index >= child_count())
     return;
   if (children_[index] == view)
     return;
@@ skipping 11 matching lines @@
   if (prev_focusable)
     prev_focusable->next_focusable_view_ = next_focusable;
   if (next_focusable)
     next_focusable->previous_focusable_view_ = prev_focusable;
 
   // Add it in the specified index now.
   InitFocusSiblings(view, index);
   children_.insert(children_.begin() + index, view);
 
   for (ViewObserver& observer : observers_)
-    observer.OnChildViewReordered(view);
+    observer.OnChildViewReordered(this, view);
 
   ReorderLayers();
 }
 
 void View::RemoveChildView(View* view) {
   DoRemoveChildView(view, true, true, false, NULL);
 }
 
 void View::RemoveAllChildViews(bool delete_children) {
   while (!children_.empty())
@@ skipping 1659 matching lines @@
 #endif
   children_.erase(i);
 
   if (update_tool_tip)
     UpdateTooltip();
 
   if (layout_manager_)
     layout_manager_->ViewRemoved(this, view);
 
   for (ViewObserver& observer : observers_)
-    observer.OnChildViewRemoved(view, this);
+    observer.OnChildViewRemoved(this, view);
 }
 
 void View::PropagateRemoveNotifications(View* old_parent,
                                         View* new_parent,
                                         bool is_removed_from_widget) {
   {
     internal::ScopedChildrenLock lock(this);
     for (auto* child : children_) {
       child->PropagateRemoveNotifications(old_parent, new_parent,
                                           is_removed_from_widget);
@@ skipping 584 matching lines @@
   // Message the RootView to do the drag and drop. That way if we're removed
   // the RootView can detect it and avoid calling us back.
   gfx::Point widget_location(event.location());
   ConvertPointToWidget(this, &widget_location);
   widget->RunShellDrag(this, data, widget_location, drag_operations, source);
   // WARNING: we may have been deleted.
   return true;
 }
 
 }  // namespace views