app_list: Fix possible out of bounds index.

ui/app_list/cocoa/apps_grid_controller_unittest.mm

Index: ui/app_list/cocoa/apps_grid_controller_unittest.mm
diff --git a/ui/app_list/cocoa/apps_grid_controller_unittest.mm b/ui/app_list/cocoa/apps_grid_controller_unittest.mm
index 13634d818b9938cf7cb6c913d43cdb04a9e22d1c..fdb5e60f6b936bb4a1de3a0ba144e2f3c908feaa 100644
--- a/ui/app_list/cocoa/apps_grid_controller_unittest.mm
+++ b/ui/app_list/cocoa/apps_grid_controller_unittest.mm
@@ -454,6 +454,7 @@ TEST_F(AppsGridControllerTest, ModelUpdate) {
   EXPECT_NSEQ(@"UpdatedItem", [button title]);
 
   // Test icon updates through the model observer by ensuring the icon changes.
+  item_model->SetIcon(gfx::ImageSkia(), false);
   NSSize icon_size = [[button image] size];
   EXPECT_EQ(0, icon_size.width);
   EXPECT_EQ(0, icon_size.height);