PPAPI: Force async callback invocation option.

ppapi/cpp/paint_manager.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ppapi/cpp/paint_manager.h"
 
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/cpp/instance.h"
 #include "ppapi/cpp/logging.h"
 #include "ppapi/cpp/module.h"
@@ skipping 115 matching lines @@
   aggregator_.ClearPendingUpdate();
 
   // Apply any scroll before asking the client to paint.
   if (update.has_scroll)
     graphics_.Scroll(update.scroll_rect, update.scroll_delta);
 
   if (!client_->OnPaint(graphics_, update.paint_rects, update.paint_bounds))
     return;  // Nothing was painted, don't schedule a flush.
 
   int32_t result = graphics_.Flush(
-      callback_factory_.NewCallback(&PaintManager::OnFlushComplete));
+      callback_factory_.NewOptionalCallback(&PaintManager::OnFlushComplete));
 
   // If you trigger this assertion, then your plugin has called Flush()
   // manually. When using the PaintManager, you should not call Flush, it will
   // handle that for you because it needs to know when it can do the next paint
   // by implementing the flush callback.
   //
   // Another possible cause of this assertion is re-using devices. If you
   // use one device, swap it with another, then swap it back, we won't know
   // that we've already scheduled a Flush on the first device. It's best to not
   // re-use devices in this way.
@@ skipping 22 matching lines @@
 
   // Just because we have a manual callback doesn't mean there are actually any
   // invalid regions. Even though we only schedule this callback when something
   // is pending, a Flush callback could have come in before this callback was
   // executed and that could have cleared the queue.
   if (aggregator_.HasPendingUpdate() && !flush_pending_)
     DoPaint();
 }
 
 }  // namespace pp