Dynamically calculate the number of extension icons to show per row in overflow

ui/views/controls/menu/menu_item_view.h

Index: ui/views/controls/menu/menu_item_view.h
diff --git a/ui/views/controls/menu/menu_item_view.h b/ui/views/controls/menu/menu_item_view.h
index 4f0ea441caa60e9eabdd3077309e947fc69151c0..86ceebacee61f56e0658290b8590006c2dd4b168 100644
--- a/ui/views/controls/menu/menu_item_view.h
+++ b/ui/views/controls/menu/menu_item_view.h
@@ -265,6 +265,11 @@ class VIEWS_EXPORT MenuItemView : public View {
   // Returns the preferred size of this item.
   virtual gfx::Size GetPreferredSize() const OVERRIDE;
 
+  // Gets the preferred height for the given |width|. This is only different
+  // from GetPreferredSize().width() if the item has a child view with flexible
+  // dimensions.
+  virtual int GetHeightForWidth(int width) const OVERRIDE;
+
   // Return the preferred dimensions of the item in pixel.
   const MenuItemDimensions& GetDimensions() const;
 
@@ -419,7 +424,7 @@ class VIEWS_EXPORT MenuItemView : public View {
   // Returns true if the menu has items with a checkbox or a radio button.
   bool HasChecksOrRadioButtons() const;
 
-  void invalidate_dimensions() { dimensions_.height = 0; }
+  void invalidate_dimensions() const { dimensions_.height = 0; }
   bool is_dimensions_valid() const { return dimensions_.height > 0; }
 
   // The delegate. This is only valid for the root menu item. You shouldn't