Add some CHECKs to track down the source of a NULL deref in the SSLClientSocketWin code.

net/socket/ssl_client_socket_win.cc

 // Copyright (c) 2006-2009 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 "net/socket/ssl_client_socket_win.h"
 
 #include <schnlsp.h>
 
 #include "base/lock.h"
 #include "base/singleton.h"
@@ skipping 525 matching lines @@
       decrypted_ptr_ = NULL;
       if (bytes_received_ != 0) {
         memmove(recv_buffer_.get(), received_ptr_, bytes_received_);
         received_ptr_ = recv_buffer_.get();
       }
     }
     return len;
   }
 
   DCHECK(!user_buf_);
+  // http://crbug.com/16371: We're seeing |buf->data()| return NULL.  See if the
+  // user is passing in an IOBuffer with a NULL |data_|.
+  CHECK(buf);
+  CHECK(buf->data());
   user_buf_ = buf;
   user_buf_len_ = buf_len;
 
   SetNextStateForRead();
   int rv = DoLoop(OK);
   if (rv == ERR_IO_PENDING) {
     user_callback_ = callback;
   } else {
     user_buf_ = NULL;
   }
@@ skipping 636 matching lines @@
   }
 }
 
 void SSLClientSocketWin::FreeSendBuffer() {
   SECURITY_STATUS status = FreeContextBuffer(send_buffer_.pvBuffer);
   DCHECK(status == SEC_E_OK);
   memset(&send_buffer_, 0, sizeof(send_buffer_));
 }
 
 }  // namespace net