Add keyboard navigation for start page tiles in experimental app list.

ui/app_list/views/start_page_view.h

 // Copyright 2014 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_APP_LIST_VIEWS_START_PAGE_VIEW_H_
 #define UI_APP_LIST_VIEWS_START_PAGE_VIEW_H_
 
 #include "base/basictypes.h"
 #include "ui/app_list/app_list_export.h"
 #include "ui/app_list/views/search_result_container_view.h"
@@ skipping 24 matching lines @@
 
   // Called when the start page view is displayed.
   void OnShow();
 
   // Called when the start page view is hidden (while the app list is still
   // open).
   void OnHide();
 
   // Overridden from views::View:
   void Layout() override;
+  bool OnKeyPressed(const ui::KeyEvent& event) override;
 
   // Overridden from SearchResultContainerView:
   void OnContainerSelected(bool from_bottom) override;
 
   // Returns search box bounds to use when the start page is active.
   gfx::Rect GetSearchBoxBounds() const;
 
   // Updates whether the custom page clickzone is visible.
   void UpdateCustomPageClickzoneVisibility();
 
@@ skipping 16 matching lines @@
 
   std::vector<SearchResultTileItemView*> search_result_tile_views_;
   AllAppsTileItemView* all_apps_button_;
 
   DISALLOW_COPY_AND_ASSIGN(StartPageView);
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_VIEWS_START_PAGE_VIEW_H_