Refactor the way singleton-style resources are exposed via PPB_Instance

ppapi/thunk/ppb_flash_functions_api.h

Index: ppapi/thunk/ppb_flash_functions_api.h
diff --git a/ppapi/thunk/ppb_flash_functions_api.h b/ppapi/thunk/ppb_flash_functions_api.h
index 73fa1184b13668a6eb175a120f2ea5f0b27fbb9b..0f7ffc60ca7047044507b5f13364e90d0f8c218f 100644
--- a/ppapi/thunk/ppb_flash_functions_api.h
+++ b/ppapi/thunk/ppb_flash_functions_api.h
@@ -5,6 +5,7 @@
 #ifndef PPAPI_THUNK_PPB_FLASH_FUNCTIONS_API_H_
 #define PPAPI_THUNK_PPB_FLASH_FUNCTIONS_API_H_
 
+#include "ppapi/shared_impl/api_id.h"
 #include "ppapi/thunk/ppapi_thunk_export.h"
 
 struct PP_ArrayOutput;
@@ -18,6 +19,8 @@ namespace thunk {
 class PPAPI_THUNK_EXPORT PPB_Flash_Functions_API {
  public:
   virtual ~PPB_Flash_Functions_API() {}
+
+  static const SingletonResourceID kSingletonResourceID = FLASH_SINGLETON_ID;
 };
 
 }  // namespace thunk