ash::ShelfView: CHECK against potentially bad static_casts.

There are a number of static downcasts in ShelfView that are *probably*
correct, but there is no clear proof that they are casting to the
correct type. This patch adds explicit CHECKs before every static_cast
to ensure that we are not casting from an incompatible dynamic type.

drag_view_ now has type ShelfButton*, so it is downcast on assignment,
rather than on many of its uses.

BUG=418460

Review URL: https://codereview.chromium.org/614653002

Cr-Commit-Position: refs/heads/master@{#297335}

ash/shelf/shelf_button.cc

@@ -204,6 +204,9 @@ ShelfButton::IconView::~IconView() {
 ////////////////////////////////////////////////////////////////////////////////
 // ShelfButton
 
+// static
+const char ShelfButton::kViewClassName[] = "ash/ShelfButton";
+
 ShelfButton* ShelfButton::Create(views::ButtonListener* listener,
                                  ShelfButtonHost* host,
                                  ShelfLayoutManager* shelf_layout_manager) {
@@ -321,6 +324,10 @@ void ShelfButton::ShowContextMenu(const gfx::Point& p,
   }
 }
 
+const char* ShelfButton::GetClassName() const {
+  return kViewClassName;
+}
+
 bool ShelfButton::OnMousePressed(const ui::MouseEvent& event) {
   CustomButton::OnMousePressed(event);
   host_->PointerPressedOnButton(this, ShelfButtonHost::MOUSE, event);

ash/shelf/shelf_button.h

@@ -17,6 +17,8 @@ class ShelfLayoutManager;
 // Button used for items on the launcher, except for the AppList.
 class ASH_EXPORT ShelfButton : public views::CustomButton {
  public:
+  static const char kViewClassName[];
+
   // Used to indicate the current state of the button.
   enum State {
     // Nothing special. Usually represents an app shortcut item with no running
@@ -91,6 +93,7 @@ class ASH_EXPORT ShelfButton : public views::CustomButton {
   };
 
   // View overrides:
+  virtual const char* GetClassName() const OVERRIDE;
   virtual bool OnMousePressed(const ui::MouseEvent& event) OVERRIDE;
   virtual void OnMouseReleased(const ui::MouseEvent& event) OVERRIDE;
   virtual bool OnMouseDragged(const ui::MouseEvent& event) OVERRIDE;

ash/shelf/shelf_view.cc

@@ -462,7 +462,9 @@ gfx::Rect ShelfView::GetIdealBoundsOfItemIcon(ShelfID id) {
     index = last_visible_index_ + 1;
   const gfx::Rect& ideal_bounds(view_model_->ideal_bounds(index));
   DCHECK_NE(TYPE_APP_LIST, model_->items()[index].type);
-  ShelfButton* button = static_cast<ShelfButton*>(view_model_->view_at(index));
+  views::View* view = view_model_->view_at(index);
+  CHECK_EQ(ShelfButton::kViewClassName, view->GetClassName());
+  ShelfButton* button = static_cast<ShelfButton*>(view);
   gfx::Rect icon_bounds = button->GetIconBounds();
   return gfx::Rect(GetMirroredXWithWidthInView(
                        ideal_bounds.x() + icon_bounds.x(), icon_bounds.width()),
@@ -1068,9 +1070,8 @@ bool ShelfView::HandleRipOffDrag(const ui::LocatedEvent& event) {
   int delta = CalculateShelfDistance(screen_location);
   if (delta > kRipOffDistance) {
     // Create a proxy view item which can be moved anywhere.
-    ShelfButton* button = static_cast<ShelfButton*>(drag_view_);
     CreateDragIconProxy(event.root_location(),
-                        button->GetImage(),
+                        drag_view_->GetImage(),
                         drag_view_,
                         gfx::Vector2d(0, 0),
                         kDragAndDropProxyScale);
@@ -1152,8 +1153,7 @@ void ShelfView::FinalizeRipOffDrag(bool cancel) {
       // animation end the flag gets cleared if |snap_back_from_rip_off_view_|
       // is set.
       snap_back_from_rip_off_view_ = drag_view_;
-      ShelfButton* button = static_cast<ShelfButton*>(drag_view_);
-      button->AddState(ShelfButton::STATE_HIDDEN);
+      drag_view_->AddState(ShelfButton::STATE_HIDDEN);
       // When a canceling drag model is happening, the view model is diverged
       // from the menu model and movements / animations should not be done.
       model_->Move(current_index, start_drag_index_);
@@ -1528,6 +1528,7 @@ void ShelfView::ShelfItemChanged(int model_index, const ShelfItem& old_item) {
     case TYPE_PLATFORM_APP:
     case TYPE_DIALOG:
     case TYPE_APP_PANEL: {
+      CHECK_EQ(ShelfButton::kViewClassName, view->GetClassName());
       ShelfButton* button = static_cast<ShelfButton*>(view);
       ReflectItemStatus(item, button);
       // The browser shortcut is currently not a "real" item and as such the
@@ -1572,7 +1573,8 @@ void ShelfView::PointerPressedOnButton(views::View* view,
   if (view_model_->view_size() <= 1 || !item_delegate->IsDraggable())
     return;  // View is being deleted or not draggable, ignore request.
 
-  drag_view_ = view;
+  CHECK_EQ(ShelfButton::kViewClassName, view->GetClassName());
+  drag_view_ = static_cast<ShelfButton*>(view);
   drag_origin_ = gfx::Point(event.x(), event.y());
   UMA_HISTOGRAM_ENUMERATION("Ash.ShelfAlignmentUsage",
       layout_manager_->SelectValueForShelfAlignment(
@@ -1866,6 +1868,7 @@ void ShelfView::OnBoundsAnimatorDone(views::BoundsAnimator* animator) {
       for (int index = 0; index < view_model_->view_size(); index++) {
         views::View* view = view_model_->view_at(index);
         if (view == snap_back_from_rip_off_view_) {
+          CHECK_EQ(ShelfButton::kViewClassName, view->GetClassName());
           ShelfButton* button = static_cast<ShelfButton*>(view);
           button->ClearState(ShelfButton::STATE_HIDDEN);
           break;

ash/shelf/shelf_view.h

@@ -356,7 +356,7 @@ class ASH_EXPORT ShelfView : public views::View,
 
   // The view being dragged. This is set immediately when the mouse is pressed.
   // |dragging_| is set only if the mouse is dragged far enough.
-  views::View* drag_view_;
+  ShelfButton* drag_view_;
 
   // Position of the mouse down event in |drag_view_|'s coordinates.
   gfx::Point drag_origin_;