PPAPI: Make blocking completion callbacks work.

ppapi/thunk/ppb_file_system_api.h

Index: ppapi/thunk/ppb_file_system_api.h
diff --git a/ppapi/thunk/ppb_file_system_api.h b/ppapi/thunk/ppb_file_system_api.h
index 096d0721235ce473cfb245a7c187111fa0babaf4..f2c80639730cc67289a301be6a203f13d6c7cdcd 100644
--- a/ppapi/thunk/ppb_file_system_api.h
+++ b/ppapi/thunk/ppb_file_system_api.h
@@ -6,6 +6,7 @@
 #define PPAPI_THUNK_PPB_FILE_SYSTEM_API_H_
 
 #include "ppapi/c/ppb_file_system.h"
+#include "ppapi/shared_impl/api_callback_type.h"
 
 namespace ppapi {
 namespace thunk {
@@ -15,7 +16,7 @@ class PPB_FileSystem_API {
   virtual ~PPB_FileSystem_API() {}
 
   virtual int32_t Open(int64_t expected_size,
-                       PP_CompletionCallback callback) = 0;
+                       ApiCallbackType callback) = 0;
   virtual PP_FileSystemType GetType() = 0;
 };