Add a warning when developing an extension that uses old manifest version.

chrome/common/extensions/manifest_tests/extension_manifest_test.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 "chrome/common/extensions/manifest_tests/extension_manifest_test.h"
 
 #include "base/file_path.h"
 #include "base/file_util.h"
 #include "base/values.h"
 #include "base/json/json_file_value_serializer.h"
@@ skipping 109 matching lines @@
     const Manifest& manifest,
     const std::string& expected_warning,
     Extension::Location location,
     int flags) {
   std::string error;
   scoped_refptr<Extension> extension =
       LoadExtension(manifest, &error, location, flags);
   EXPECT_TRUE(extension) << manifest.name();
   EXPECT_EQ("", error) << manifest.name();
   EXPECT_EQ(1u, extension->install_warnings().size());
-  EXPECT_EQ(expected_warning, extension->install_warnings()[0]);
+  EXPECT_EQ(expected_warning, extension->install_warnings()[0].message);
   return extension;
 }
 
 scoped_refptr<Extension> ExtensionManifestTest::LoadAndExpectWarning(
     char const* manifest_name,
     const std::string& expected_warning,
     Extension::Location location,
     int flags) {
   return LoadAndExpectWarning(
       Manifest(manifest_name), expected_warning, location, flags);
@@ skipping 93 matching lines @@
       break;
     case EXPECT_TYPE_SUCCESS:
       for (size_t i = 0; i < num_testcases; ++i) {
         LoadAndExpectSuccess(testcases[i].manifest_filename_.c_str(),
                              testcases[i].location_,
                              testcases[i].flags_);
       }
       break;
    }
 }