Add support for an optional "requirements" section in extension/app manifests.

chrome/common/extensions/extension_constants.h

 // Copyright (c) 2011 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_EXTENSION_CONSTANTS_H_
 #define CHROME_COMMON_EXTENSIONS_EXTENSION_CONSTANTS_H_
 #pragma once
 
 #include <string>
 
@@ skipping 63 matching lines @@
   extern const char* kPageActionId;
   extern const char* kPageActionPopup;
   extern const char* kPageActionPopupHeight;
   extern const char* kPageActionPopupPath;
   extern const char* kPageActions;
   extern const char* kPermissions;
   extern const char* kPlugins;
   extern const char* kPluginsPath;
   extern const char* kPluginsPublic;
   extern const char* kPublicKey;
+  extern const char* kRequirements;
   extern const char* kRunAt;
   extern const char* kShiftKey;
   extern const char* kShortcutKey;
   extern const char* kSidebar;
   extern const char* kSidebarDefaultIcon;
   extern const char* kSidebarDefaultPage;
   extern const char* kSidebarDefaultTitle;
   extern const char* kSignature;
   extern const char* kTheme;
   extern const char* kThemeColors;
@@ skipping 133 matching lines @@
   extern const char* kInvalidPageActionPopupPath;
   extern const char* kInvalidPageActionsList;
   extern const char* kInvalidPageActionsListSize;
   extern const char* kInvalidPageActionTypeValue;
   extern const char* kInvalidPermission;
   extern const char* kInvalidPermissions;
   extern const char* kInvalidPermissionScheme;
   extern const char* kInvalidPlugins;
   extern const char* kInvalidPluginsPath;
   extern const char* kInvalidPluginsPublic;
+  extern const char* kInvalidRequirement;
+  extern const char* kInvalidRequirements;
   extern const char* kInvalidRunAt;
   extern const char* kInvalidSidebar;
   extern const char* kInvalidSidebarDefaultIconPath;
   extern const char* kInvalidSidebarDefaultPage;
   extern const char* kInvalidSidebarDefaultTitle;
   extern const char* kInvalidSignature;
   extern const char* kInvalidTheme;
   extern const char* kInvalidThemeColors;
   extern const char* kInvalidThemeImages;
   extern const char* kInvalidThemeImagesMissing;
@@ skipping 210 matching lines @@
   };
 
   enum UnloadedExtensionReason {
     UNLOAD_REASON_DISABLE,    // Extension is being disabled.
     UNLOAD_REASON_UPDATE,     // Extension is being updated to a newer version.
     UNLOAD_REASON_UNINSTALL,  // Extension is being uninstalled.
   };
 } // extension_misc
 
 #endif  // CHROME_COMMON_EXTENSIONS_EXTENSION_CONSTANTS_H_