Add a showcase entry for the content widget.

ios/showcase/core/showcase_model.mm

Index: ios/showcase/core/showcase_model.mm
diff --git a/ios/showcase/core/showcase_model.mm b/ios/showcase/core/showcase_model.mm
index 491b6ade8606e8690fd5eaba4f9008a1cb0af70b..51bd3f439dbf2d933cec5b44aefe1bb6293e688f 100644
--- a/ios/showcase/core/showcase_model.mm
+++ b/ios/showcase/core/showcase_model.mm
@@ -86,6 +86,11 @@
       showcase::kClassForInstantiationKey : @"SCSearchWidgetCoordinator",
       showcase::kUseCaseKey : @"Search Widget",
     },
+    @{
+      showcase::kClassForDisplayKey : @"ContentWidgetViewController",
+      showcase::kClassForInstantiationKey : @"SCContentWidgetCoordinator",
+      showcase::kUseCaseKey : @"Content Widget",
+    },
   ];
 }