Allow manifest handlers to declare keys they depend on that must be parsed before them.

chrome/common/extensions/manifest_handler.h

 // Copyright (c) 2013 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_MANIFEST_HANDLER_H_
 #define CHROME_COMMON_EXTENSIONS_MANIFEST_HANDLER_H_
 
 #include <set>
 #include <string>
 
+#include "base/memory/linked_ptr.h"
 #include "base/string16.h"
 #include "chrome/common/extensions/extension.h"
 #include "chrome/common/extensions/manifest.h"
 
 namespace extensions {
 
 class ManifestHandler {
  public:
   ManifestHandler();
   virtual ~ManifestHandler();
 
   // Attempts to parse the extension's manifest.
   // Returns true on success or false on failure; if false, |error| will
   // be set to a failure message.
   virtual bool Parse(Extension* extension, string16* error) = 0;
 
   // If false (the default), only parse the manifest if a registered
   // key is present in the manifest. If true, always attempt to parse
   // the manifest for this extension type, even if no registered keys
   // are present. This allows specifying a default parsed value for
   // extensions that don't declare our key in the manifest.
   // TODO(yoz): Use Feature availability instead.
   virtual bool AlwaysParseForType(Manifest::Type type);
 
+  // The list of keys that, if present, should be parsed before calling our
+  // Parse (typically, because our Parse needs to read those keys).
+  // Defaults to empty.
+  virtual const std::vector<std::string>& PrerequisiteKeys();
+
   // Associate |handler| with |key| in the manifest. A handler can register
   // for multiple keys. The global registry takes ownership of |handler|;
   // if it has an existing handler for |key|, it replaces it with this one.
   //
   // WARNING: Manifest handlers registered only in the browser process
   // are not available to renderers or utility processes.
-  static void Register(const std::string& key, ManifestHandler* handler);
+  static void Register(const std::string& key,
+                       linked_ptr<ManifestHandler> handler);
 
   // Call Parse on all registered manifest handlers that should parse
   // this extension.
   static bool ParseExtension(Extension* extension, string16* error);
+
+  // Reset the manifest handler registry to an empty state. Useful for
+  // unit tests.
+  static void ClearRegistryForTesting();
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_COMMON_EXTENSIONS_MANIFEST_HANDLER_H_