PPAPI: Force async callback invocation option.

ppapi/cpp/completion_callback.h

Index: ppapi/cpp/completion_callback.h
===================================================================
--- ppapi/cpp/completion_callback.h	(revision 82761)
+++ ppapi/cpp/completion_callback.h	(working copy)
@@ -27,6 +27,8 @@
     cc_ = PP_MakeCompletionCallback(func, user_data);
   }
 
+  void set_flags(int32_t flags) { cc_.flags = flags; }
+
   // Call this method to explicitly run the CompletionCallback.  Normally, the
   // system runs a CompletionCallback after an asynchronous operation
   // completes, but programs may wish to run the CompletionCallback manually
@@ -69,8 +71,7 @@
 //     void ProcessFile(const FileRef& file) {
 //       CompletionCallback cc = factory_.NewCallback(&MyHandler::DidOpen);
 //       int32_t rv = fio_.Open(file, PP_FileOpenFlag_Read, cc);
-//       if (rv != PP_OK_COMPLETIONPENDING)
-//         cc.Run(rv);
+//       CHECK(rv == PP_OK_COMPLETIONPENDING);
 //     }
 //
 //    private:
@@ -101,6 +102,7 @@
 //
 //     void ReadMore() {
 //       CompletionCallback cc = factory_.NewCallback(&MyHandler::DidRead);
+//       cc.set_flags(PP_COMPLETIONCALLBACK_FLAG_NOFORCEASYNC);
 //       int32_t rv = fio_.Read(offset_, buf_, sizeof(buf_),
 //                              cc.pp_completion_callback());
 //       if (rv != PP_OK_COMPLETIONPENDING)