Prevent duplicate concurrent installs of the same extension

chrome/browser/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_BROWSER_EXTENSIONS_WEBSTORE_INSTALL_RESULT_H_
 #define CHROME_BROWSER_EXTENSIONS_WEBSTORE_INSTALL_RESULT_H_
 
 namespace extensions {
 
 namespace webstore_install {
 
 // Result codes returned by WebstoreStandaloneInstaller and its subclasses.
 enum Result {
   // Successful operation.
   SUCCESS,
 
   // Unknown error.
   UNKNOWN_ERROR,
 
   // The operation was aborted as the requestor is no longer alive.
   ABORTED,
 
+  // An installation of the same extension is in progress.
+  INSTALL_IN_PROGRESS,
+
   // The installation is not permitted.
   NOT_PERMITTED,
 
   // Invalid Chrome Web Store item ID.
   INVALID_ID,
 
   // Failed to retrieve extension metadata from the Web Store.
   WEBSTORE_REQUEST_ERROR,
 
   // The extension metadata retrieved from the Web Store was invalid.
@@ skipping 19 matching lines @@
   // Unsatisfied requirements, such as webgl.
   REQUIREMENT_VIOLATIONS,
 
   // The extension is blocked by management policies.
   BLOCKED_BY_POLICY,
 
   // The launch feature is not available.
   LAUNCH_FEATURE_DISABLED,
 
   // The launch feature is not supported for the extension type.
-  LAUNCH_UNSUPPORTED_EXTENSION_TYPE
+  LAUNCH_UNSUPPORTED_EXTENSION_TYPE,
+
+  // A launch of the same extension is in progress.
+  LAUNCH_IN_PROGRESS
 };
 
 }  // namespace webstore_install
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_WEBSTORE_INSTALL_RESULT_H_