ui: Change ListModel to operate in size_t instead of int.

ui/app_list/app_list_model_view.h

Index: ui/app_list/app_list_model_view.h
diff --git a/ui/app_list/app_list_model_view.h b/ui/app_list/app_list_model_view.h
index a0c9fa1caabc83fa82e66d009e0096406540e84f..89fc7f6f4a5f7550148fe4ed6cc11004b0b69d51 100644
--- a/ui/app_list/app_list_model_view.h
+++ b/ui/app_list/app_list_model_view.h
@@ -71,9 +71,9 @@ class APP_LIST_EXPORT AppListModelView : public views::View,
   virtual void OnPaintFocusBorder(gfx::Canvas* canvas) OVERRIDE;
 
   // Overridden from ListModelObserver:
-  virtual void ListItemsAdded(int start, int count) OVERRIDE;
-  virtual void ListItemsRemoved(int start, int count) OVERRIDE;
-  virtual void ListItemsChanged(int start, int count) OVERRIDE;
+  virtual void ListItemsAdded(size_t start, size_t count) OVERRIDE;
+  virtual void ListItemsRemoved(size_t start, size_t count) OVERRIDE;
+  virtual void ListItemsChanged(size_t start, size_t count) OVERRIDE;
 
   // Overridden from PaginationModelObserver:
   virtual void TotalPagesChanged() OVERRIDE;