Put the null pointer check for theme images before we use the

chrome/browser/extensions/extension_file_util.cc

 // Copyright (c) 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 "chrome/browser/extensions/extension_file_util.h"
 
 #include "base/file_util.h"
 #include "base/logging.h"
 #include "base/scoped_temp_dir.h"
 #include "base/string_util.h"
@@ skipping 178 matching lines @@
     if (!file_util::PathExists(extension->GetResourcePath(iter->second))) {
       *error = StringPrintf("Could not load extension icon '%s'.",
                             iter->second.c_str());
       return NULL;
     }
   }
 
   // Theme resource validation.
   if (extension->IsTheme()) {
     DictionaryValue* images_value = extension->GetThemeImages();
-    DictionaryValue::key_iterator iter = images_value->begin_keys();
     if (images_value) {
+      DictionaryValue::key_iterator iter = images_value->begin_keys();
       while (iter != images_value->end_keys()) {
         std::string val;
         if (images_value->GetString(*iter , &val)) {
           FilePath image_path = extension->path().AppendASCII(val);
           if (!file_util::PathExists(image_path)) {
             *error = StringPrintf(
                 "Could not load '%s' for theme.",
                 WideToUTF8(image_path.ToWStringHack()).c_str());
             return NULL;
           }
@@ skipping 122 matching lines @@
                       "directory: " << extension_id;
       LOG(INFO) << "Deleting invalid extension directory "
                 << WideToASCII(extension_path.ToWStringHack()) << ".";
       file_util::Delete(extension_path, true);  // Recursive.
       continue;
     }
   }
 }
 
 }  // extensionfile_util