Refactor app list so AppsGridView owns the PaginationModel.

ui/app_list/views/page_switcher.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.
 
 #include "ui/app_list/views/page_switcher.h"
 
 #include <algorithm>
 
 #include "third_party/skia/include/core/SkPath.h"
 #include "ui/app_list/app_list_constants.h"
@@ skipping 110 matching lines @@
     : model_(model),
       buttons_(new views::View) {
   AddChildView(buttons_);
 
   TotalPagesChanged();
   SelectedPageChanged(-1, model->selected_page());
   model_->AddObserver(this);
 }
 
 PageSwitcher::~PageSwitcher() {
-  model_->RemoveObserver(this);
+  if (model_)
+    model_->RemoveObserver(this);
 }
 
 int PageSwitcher::GetPageForPoint(const gfx::Point& point) const {
   if (!buttons_->bounds().Contains(point))
     return -1;
 
   gfx::Point buttons_point(point);
   views::View::ConvertPointToTarget(this, buttons_, &buttons_point);
 
   for (int i = 0; i < buttons_->child_count(); ++i) {
@@ skipping 16 matching lines @@
     return;
   }
 
   for (int i = 0; i < button_count; ++i) {
     PageSwitcherButton* button =
         static_cast<PageSwitcherButton*>(buttons_->child_at(i));
     button->SetState(views::CustomButton::STATE_NORMAL);
   }
 }
 
+void PageSwitcher::ReleasePaginationModel() {
+  if (!model_)
+    return;
+  model_->RemoveObserver(this);
+  model_ = NULL;
+}
+
 gfx::Size PageSwitcher::GetPreferredSize() const {
   // Always return a size with correct height so that container resize is not
   // needed when more pages are added.
   return gfx::Size(buttons_->GetPreferredSize().width(),
                    kPreferredHeight);
 }
 
 void PageSwitcher::Layout() {
   gfx::Rect rect(GetContentsBounds());
 
@@ skipping 33 matching lines @@
       views::BoxLayout::kHorizontal, kButtonStripPadding, 0, button_spacing));
   for (int i = 0; i < button_count; ++i) {
     PageSwitcherButton* button =
         static_cast<PageSwitcherButton*>(buttons_->child_at(i));
     button->set_button_width(button_width);
   }
 }
 
 void PageSwitcher::ButtonPressed(views::Button* sender,
                                  const ui::Event& event) {
+  if (!model_)
+    return;
+
   for (int i = 0; i < buttons_->child_count(); ++i) {
     if (sender == static_cast<views::Button*>(buttons_->child_at(i))) {
       model_->SelectPage(i, true /* animate */);
       break;
     }
   }
 }
 
 void PageSwitcher::TotalPagesChanged() {
+  DCHECK(model_);
   buttons_->RemoveAllChildViews(true);
   for (int i = 0; i < model_->total_pages(); ++i) {
     PageSwitcherButton* button = new PageSwitcherButton(this);
     button->SetSelectedRange(i == model_->selected_page() ? 1 : 0);
     buttons_->AddChildView(button);
   }
   buttons_->SetVisible(model_->total_pages() > 1);
   Layout();
 }
 
 void PageSwitcher::SelectedPageChanged(int old_selected, int new_selected) {
   if (old_selected >= 0 && old_selected < buttons_->child_count())
     GetButtonByIndex(buttons_, old_selected)->SetSelectedRange(0);
   if (new_selected >= 0 && new_selected < buttons_->child_count())
     GetButtonByIndex(buttons_, new_selected)->SetSelectedRange(1);
 }
 
 void PageSwitcher::TransitionStarted() {
 }
 
 void PageSwitcher::TransitionChanged() {
+  DCHECK(model_);
   const int current_page = model_->selected_page();
   const int target_page = model_->transition().target_page;
 
   double progress = model_->transition().progress;
   double remaining = progress - 1;
 
   if (current_page > target_page) {
     remaining = -remaining;
     progress = -progress;
   }
 
   GetButtonByIndex(buttons_, current_page)->SetSelectedRange(remaining);
   if (model_->is_valid_page(target_page))
     GetButtonByIndex(buttons_, target_page)->SetSelectedRange(progress);
 }
 
 }  // namespace app_list