ash::ShelfView: CHECK against potentially bad static_casts.

ash/shelf/shelf_button.cc

Index: ash/shelf/shelf_button.cc
diff --git a/ash/shelf/shelf_button.cc b/ash/shelf/shelf_button.cc
index b244a9d4ced75536d1b98e0af2c0c53a8d7a12ba..1aba1ccb4357845983fbcfcb45079b0171686eca 100644
--- a/ash/shelf/shelf_button.cc
+++ b/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);