Fix a crash in the code which attempts to append the user agent to the list o...

chrome_frame/http_negotiate.cc

 // Copyright (c) 2010 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 "chrome_frame/http_negotiate.h"
 
 #include <atlbase.h>
 #include <atlcom.h>
 #include <htiframe.h>
 
@@ skipping 117 matching lines @@
   new_headers += "User-Agent: " + user_agent_value;
   new_headers += "\r\n";
   return new_headers;
 }
 
 std::string ReplaceOrAddUserAgent(LPCWSTR headers,
                                   const std::string& user_agent_value) {
   DCHECK(headers);
   using net::HttpUtil;
 
-  std::string ascii_headers(WideToASCII(headers));
+  if (headers) {
+    std::string ascii_headers(WideToASCII(headers));
 
-  // Extract "User-Agent" from the headers.
-  HttpUtil::HeadersIterator headers_iterator(ascii_headers.begin(),
-                                             ascii_headers.end(), "\r\n");
+    // Extract "User-Agent" from the headers.
+    HttpUtil::HeadersIterator headers_iterator(ascii_headers.begin(),
+                                               ascii_headers.end(), "\r\n");
 
-  // Build new headers, skip the existing user agent value from
-  // existing headers.
-  std::string new_headers;
-  while (headers_iterator.GetNext()) {
-    std::string name(headers_iterator.name());
-    if (!LowerCaseEqualsASCII(name, kLowerCaseUserAgent)) {
-      new_headers += name + ": " + headers_iterator.values() + "\r\n";
+    // Build new headers, skip the existing user agent value from
+    // existing headers.
+    std::string new_headers;
+    while (headers_iterator.GetNext()) {
+      std::string name(headers_iterator.name());
+      if (!LowerCaseEqualsASCII(name, kLowerCaseUserAgent)) {
+        new_headers += name + ": " + headers_iterator.values() + "\r\n";
+      }
     }
   }
-
   new_headers += "User-Agent: " + user_agent_value;
   new_headers += "\r\n";
   return new_headers;
 }
 
 HttpNegotiatePatch::HttpNegotiatePatch() {
 }
 
 HttpNegotiatePatch::~HttpNegotiatePatch() {
 }
@@ skipping 64 matching lines @@
     DLOG(WARNING) << __FUNCTION__ << " Delegate returned an error";
     return hr;
   }
   std::string updated(AppendCFUserAgentString(headers, *additional_headers));
   *additional_headers = reinterpret_cast<wchar_t*>(::CoTaskMemRealloc(
       *additional_headers, (updated.length() + 1) * sizeof(wchar_t)));
   lstrcpyW(*additional_headers, ASCIIToWide(updated).c_str());
   return S_OK;
 }