Refactor the way singleton-style resources are exposed via PPB_Instance

ppapi/thunk/ppb_flash_clipboard_api.h

Index: ppapi/thunk/ppb_flash_clipboard_api.h
diff --git a/ppapi/thunk/ppb_flash_clipboard_api.h b/ppapi/thunk/ppb_flash_clipboard_api.h
index ef022c4a7c17cb7c94ccb870dd5796b0ca138fb4..56025faecff4943f8d5b9690b7fb7282b1652d86 100644
--- a/ppapi/thunk/ppb_flash_clipboard_api.h
+++ b/ppapi/thunk/ppb_flash_clipboard_api.h
@@ -5,6 +5,7 @@
 #ifndef PPAPI_THUNK_PPB_FLASH_CLIPBOARD_API_H_
 #define PPAPI_THUNK_PPB_FLASH_CLIPBOARD_API_H_
 
+#include "ppapi/shared_impl/api_id.h"
 #include "ppapi/c/private/ppb_flash_clipboard.h"
 
 namespace ppapi {
@@ -32,6 +33,9 @@ class PPB_Flash_Clipboard_API {
     uint32_t data_item_count,
     const uint32_t formats[],
     const PP_Var data_items[]) = 0;
+
+  static const SingletonResourceID kSingletonResourceID =
+      FLASH_CLIPBOARD_SINGLETON_ID;
 };
 
 }  // namespace thunk