Enable size_t to int truncation warnings in PPAPI

ppapi/tests/test_tcp_socket_private.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_tcp_socket_private.h"
 
 #include <stdlib.h>
 
 #include <new>
 
@@ skipping 228 matching lines @@
   }
   return PP_ERROR_FAILED;
 }
 
 int32_t TestTCPSocketPrivate::WriteStringToSocket(pp::TCPSocketPrivate* socket,
                                                   const std::string& s) {
   const char* buffer = s.data();
   size_t written = 0;
   while (written < s.size()) {
     TestCompletionCallback cb(instance_->pp_instance(), callback_type());
-    int32_t rv = socket->Write(buffer + written, s.size() - written,
+    int32_t rv = socket->Write(buffer + written,
+                               static_cast<int32_t>(s.size() - written),
                                cb.GetCallback());
     if (callback_type() == PP_REQUIRED && rv != PP_OK_COMPLETIONPENDING)
       return PP_ERROR_FAILED;
     cb.WaitForResult(rv);
     if (cb.result() < 0)
       return cb.result();
     if (cb.result() == 0)
       return PP_ERROR_FAILED;
     written += cb.result();
   }
   if (written != s.size())
     return PP_ERROR_FAILED;
   return PP_OK;
 }