Fix PPAPINaClNewlibTest.PostMessage flakiness

ppapi/tests/test_post_message.cc

 // 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.
 
 #include "ppapi/tests/test_post_message.h"
 
 #include <string.h>
 #include <algorithm>
 #include <map>
 #include <sstream>
@@ skipping 293 matching lines @@
     ASSERT_TRUE(message_data_.back().is_bool());
     if (!message_data_.back().AsBool())
       return std::string("Failed: ") + *iter;
     ASSERT_TRUE(message_data_.back().AsBool());
     ASSERT_TRUE(ClearListeners());
   }
   PASS();
 }
 
 std::string TestPostMessage::TestSendInInit() {
-  ASSERT_EQ(1, WaitForMessages());
+  // Wait for the messages from Init() to be guaranteed to be sent.
+  WaitForMessages();
   // This test assumes Init already sent a message.
   ASSERT_EQ(1, message_data_.size());
   ASSERT_TRUE(message_data_.back().is_string());
   ASSERT_EQ(kTestString, message_data_.back().AsString());
   message_data_.clear();
   PASS();
 }
 
 std::string TestPostMessage::TestSendingData() {
   // Clean up after previous tests. This also swallows the message sent by Init
@@ skipping 575 matching lines @@
     ASSERT_TRUE(received_value <= kThreadsToRun);
     ++received_counts[received_value];
   }
   ASSERT_EQ(expected_counts, received_counts);
 
   message_data_.clear();
   ASSERT_TRUE(ClearListeners());
 
   PASS();
 }