Refactor the way singleton-style resources are exposed via PPB_Instance

ppapi/shared_impl/api_id.h

Index: ppapi/shared_impl/api_id.h
diff --git a/ppapi/shared_impl/api_id.h b/ppapi/shared_impl/api_id.h
index 360b8cbfa96848328e58faa99d42a77d17990124..61dd13c03aa5ec812f1b62052542241097baee8a 100644
--- a/ppapi/shared_impl/api_id.h
+++ b/ppapi/shared_impl/api_id.h
@@ -75,6 +75,14 @@ enum ApiID {
   API_ID_COUNT
 };
 
+// These IDs are used to access singleton resource objects using
+// PPB_Instance_API.GetSingletonResource.
+enum SingletonResourceID {
+  FLASH_SINGLETON_ID,
+  FLASH_CLIPBOARD_SINGLETON_ID,
+  GAMEPAD_SINGLETON_ID,
+};
+
 }  // namespace ppapi
 
 #endif  // PPAPI_SHARED_IMPL_API_ID_H_