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

chrome/browser/ui/views/ash/app_list/app_list_model_builder_unittest.cc

Index: chrome/browser/ui/views/ash/app_list/app_list_model_builder_unittest.cc
diff --git a/chrome/browser/ui/views/ash/app_list/app_list_model_builder_unittest.cc b/chrome/browser/ui/views/ash/app_list/app_list_model_builder_unittest.cc
index c2a176ee181b5f322c421f7d43c5546937e7a18f..37b5dfa8045550d4eba94133926c6b5ef1ecab62 100644
--- a/chrome/browser/ui/views/ash/app_list/app_list_model_builder_unittest.cc
+++ b/chrome/browser/ui/views/ash/app_list/app_list_model_builder_unittest.cc
@@ -29,7 +29,7 @@ class TestAppListItemModel : public app_list::AppListItemModel {
 // Get a string of all items in |model| joined with ','.
 std::string GetModelContent(app_list::AppListModel* model) {
   std::string content;
-  for (int i = 0; i < model->item_count(); ++i) {
+  for (size_t i = 0; i < model->item_count(); ++i) {
     if (i > 0)
       content += ',';
     content += model->GetItemAt(i)->title();