[ash-md] Adds support for gesture to move selection in overview mode

ash/common/wm/overview/window_grid.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 ASH_COMMON_WM_OVERVIEW_WINDOW_GRID_H_
 #define ASH_COMMON_WM_OVERVIEW_WINDOW_GRID_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 87 matching lines @@
   // selected the implementation fades out |selection_widget_| to transparent
   // opacity, effectively hiding the selector widget.
   void WindowClosing(WindowSelectorItem* window);
 
   // Returns true if the grid has no more windows.
   bool empty() const { return window_list_.empty(); }
 
   // Returns how many window selector items are in the grid.
   size_t size() const { return window_list_.size(); }
 
+  void set_skip_first(bool skip_first) { skip_first_ = skip_first; }
+
   // Returns true if the selection widget is active.
   bool is_selecting() const { return selection_widget_ != nullptr; }
 
   // Returns the root window in which the grid displays the windows.
   const WmWindow* root_window() const { return root_window_; }
 
   const std::vector<std::unique_ptr<WindowSelectorItem>>& window_list() const {
     return window_list_;
   }
 
@@ skipping 65 matching lines @@
 
   // Current selected window position.
   size_t selected_index_;
 
   // Number of columns in the grid.
   size_t num_columns_;
 
   // True only after all windows have been prepared for overview.
   bool prepared_for_overview_;
 
+  // True initially for the first non-empty grid and reset to false after
+  // selector has been moved at least once. Always false for all other grids.
+  bool skip_first_;
+
   DISALLOW_COPY_AND_ASSIGN(WindowGrid);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_WM_OVERVIEW_WINDOW_GRID_H_