[Extensions] Rework inline installation observation

chrome/common/extensions/webstore_install_result.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_WEBSTORE_INSTALL_RESULT_H_
 #define CHROME_COMMON_EXTENSIONS_WEBSTORE_INSTALL_RESULT_H_
 
 namespace extensions {
 
 namespace webstore_install {
 
+extern const char kInvalidWebstoreItemId[];
+extern const char kWebstoreRequestError[];
+extern const char kInvalidWebstoreResponseError[];
+extern const char kInvalidManifestError[];
+extern const char kUserCancelledError[];
+extern const char kExtensionIsBlacklisted[];
+extern const char kInstallInProgressError[];
+
 // Result codes returned by WebstoreStandaloneInstaller and its subclasses.
 enum Result {
   // Successful operation.
   SUCCESS,
 
   // Unknown error.
   OTHER_ERROR,
 
   // The operation was aborted as the requestor is no longer alive.
   ABORTED,
@@ skipping 48 matching lines @@
   // The final (and unused) result type for enum verification.
   // New results should go above this entry, and this entry should be updated.
   RESULT_LAST = LAUNCH_IN_PROGRESS,
 };
 
 }  // namespace webstore_install
 
 }  // namespace extensions
 
 #endif  // CHROME_COMMON_EXTENSIONS_WEBSTORE_INSTALL_RESULT_H_