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

ash/common/wm/overview/window_grid.h

Index: ash/common/wm/overview/window_grid.h
diff --git a/ash/common/wm/overview/window_grid.h b/ash/common/wm/overview/window_grid.h
index a18f6a60d3984958a444aafde069e16f0702f470..58957481659a11471abc12094b36a88189307594 100644
--- a/ash/common/wm/overview/window_grid.h
+++ b/ash/common/wm/overview/window_grid.h
@@ -105,6 +105,8 @@ class ASH_EXPORT WindowGrid : public WmWindowObserver,
   // 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; }
 
@@ -190,6 +192,10 @@ class ASH_EXPORT WindowGrid : public WmWindowObserver,
   // 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);
 };