PPAPI: Disallow blocking callbacks while handling a blocking message

ppapi/shared_impl/ppb_message_loop_shared.h

 // Copyright (c) 2012 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.
 
 #ifndef PPAPI_SHARED_IMPL_PPB_MESSAGE_LOOP_SHARED_H_
 #define PPAPI_SHARED_IMPL_PPB_MESSAGE_LOOP_SHARED_H_
 
 #include "base/basictypes.h"
 #include "base/callback_forward.h"
 #include "base/location.h"
@@ skipping 32 matching lines @@
   // if there isn't.
   // NOTE: The given closure will be run *WITHOUT* acquiring the Proxy lock.
   //       This only makes sense for user code and completely thread-safe
   //       proxy operations (e.g., MessageLoop::QuitClosure).
   virtual void PostClosure(const tracked_objects::Location& from_here,
                            const base::Closure& closure,
                            int64 delay_ms) = 0;
 
   virtual base::MessageLoopProxy* GetMessageLoopProxy() = 0;
 
+  // Returns whether this MessageLoop is currently handling a blocking message
+  // from JavaScript. This is used to make it illegal to use blocking callbacks
+  // while the thread is handling a blocking message.
+  virtual bool CurrentlyHandlingBlockingMessage() = 0;
+
   DISALLOW_COPY_AND_ASSIGN(MessageLoopShared);
 };
 
 }  // namespace ppapi
 
 #endif  // PPAPI_SHARED_IMPL_PPB_MESSAGE_LOOP_SHARED_H_