PPAPI: Add more error testing for postMessageAndAwaitResponse

ppapi/tests/test_message_handler.h

 // Copyright 2014 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_TESTS_TEST_MESSAGE_HANDLER_H_
 #define PPAPI_TESTS_TEST_MESSAGE_HANDLER_H_
 
 #include <string>
 #include <vector>
 
 #include "ppapi/c/ppb_messaging.h"
 #include "ppapi/tests/test_case.h"
+#include "ppapi/tests/test_utils.h"
 #include "ppapi/utility/threading/simple_thread.h"
 
 class TestMessageHandler : public TestCase {
  public:
   explicit TestMessageHandler(TestingInstance* instance);
   virtual ~TestMessageHandler();
 
  private:
   // TestCase implementation.
   virtual bool Init();
   virtual void RunTests(const std::string& filter);
   virtual void HandleMessage(const pp::Var& message_data);
 
   std::string TestRegisterErrorConditions();
   std::string TestPostMessageAndAwaitResponse();
+  std::string TestExceptions();
 
   const PPB_Messaging_1_2* ppb_messaging_if_;
   pp::SimpleThread handler_thread_;
+
+  // For TestExceptions():
+  bool testing_exceptions_;
+  NestedEvent message_received_;
+  std::string last_message_;
 };
 
 #endif  // PPAPI_TESTS_TEST_MESSAGE_HANDLER_H_