Introduce a stable set of errors for inline install

chrome/common/extensions/api/webstore/webstore_api_constants.h

 // Copyright 2014 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.
 
 #ifndef CHROME_COMMON_EXTENSIONS_API_WEBSTORE_WEBSTORE_API_CONSTANTS_H_
 #define CHROME_COMMON_EXTENSIONS_API_WEBSTORE_WEBSTORE_API_CONSTANTS_H_
 
 namespace extensions {
 namespace api {
 namespace webstore {
 
 // An enum for listener types. This is used when creating/reading the mask for
 // IPC messages.
 enum ListenerType {
   INSTALL_STAGE_LISTENER = 1,
   DOWNLOAD_PROGRESS_LISTENER = 1 << 1
 };
 
 // An enum to represent which stage the installation is in.
 enum InstallStage {
   INSTALL_STAGE_DOWNLOADING = 0,
   INSTALL_STAGE_INSTALLING,
 };
 
+// Result codes returned by WebstoreStandaloneInstaller and its subclasses.
+// IMPORTANT: Keep this list in sync with both the definition in
+// chrome/common/extensions/api/webstore.json and
+// chrome/common/extensions/webstore_install_result.h!
+extern const char* kInstallResultCodes[];
+
 extern const char kInstallStageDownloading[];
 extern const char kInstallStageInstalling[];
 extern const char kOnInstallStageChangedMethodName[];
 extern const char kOnDownloadProgressMethodName[];
 
 }  // namespace webstore
 }  // namespace api
 }  // namespace extensions
 
 #endif  // CHROME_COMMON_EXTENSIONS_API_WEBSTORE_WEBSTORE_API_CONSTANTS_H_