Content Verification: Don't access UI-thread objects on the IO thread

extensions/browser/content_hash_fetcher.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 EXTENSIONS_BROWSER_CONTENT_HASH_FETCHER_H_
 #define EXTENSIONS_BROWSER_CONTENT_HASH_FETCHER_H_
 
 #include <set>
 #include <string>
 
 #include "base/callback.h"
 #include "base/files/file_path.h"
 #include "base/memory/weak_ptr.h"
-#include "base/scoped_observer.h"
-#include "extensions/browser/content_verifier_delegate.h"
-#include "extensions/browser/extension_registry_observer.h"
 #include "extensions/common/extension.h"
 
 namespace content {
 class BrowserContext;
 }
 
 namespace extensions {
 
 class ExtensionRegistry;
 class ContentHashFetcherJob;
+class ContentVerifierDelegate;
 
 // This class is responsible for getting signed expected hashes for use in
 // extension content verification. As extensions are loaded it will fetch and
 // parse/validate/cache this data as needed, including calculating expected
 // hashes for each block of each file within an extension. (These unsigned leaf
 // node block level hashes will always be checked at time of use use to make
 // sure they match the signed treehash root hash).
-class ContentHashFetcher : public ExtensionRegistryObserver {
+class ContentHashFetcher {
  public:
   // A callback for when a fetch is complete. This reports back:
   // -extension id
   // -whether we were successful or not (have verified_contents.json and
   // -computed_hashes.json files)
   // -was it a forced check?
   // -a set of paths whose contents didn't match expected values
   typedef base::Callback<
       void(const std::string&, bool, bool, const std::set<base::FilePath>&)>
       FetchCallback;
 
   // The consumer of this class needs to ensure that context and delegate
   // outlive this object.
   ContentHashFetcher(content::BrowserContext* context,
                      ContentVerifierDelegate* delegate,
                      const FetchCallback& callback);
   virtual ~ContentHashFetcher();
 
-  // Begins the process of trying to fetch any needed verified contents, and
-  // listening for extension load/unload.
-  void Start();
-
   // Explicitly ask to fetch hashes for |extension|. If |force| is true,
   // we will always check the validity of the verified_contents.json and
   // re-check the contents of the files in the filesystem.
   void DoFetch(const Extension* extension, bool force);
 
-  // ExtensionRegistryObserver interface
-  virtual void OnExtensionLoaded(content::BrowserContext* browser_context,
-                                 const Extension* extension) OVERRIDE;
-  virtual void OnExtensionUnloaded(
-      content::BrowserContext* browser_context,
-      const Extension* extension,
-      UnloadedExtensionInfo::Reason reason) OVERRIDE;
+  // These should be called when an extension is loaded or unloaded.
+  virtual void ExtensionLoaded(const Extension* extension);
+  virtual void ExtensionUnloaded(const Extension* extension);
 
  private:
   // Callback for when a job getting content hashes has completed.
   void JobFinished(ContentHashFetcherJob* job);
 
   content::BrowserContext* context_;
   ContentVerifierDelegate* delegate_;
   FetchCallback fetch_callback_;
 
   // We keep around pointers to in-progress jobs, both so we can avoid
   // scheduling duplicate work if fetching is already in progress, and so that
   // we can cancel in-progress work at shutdown time.
   typedef std::pair<ExtensionId, std::string> IdAndVersion;
   typedef std::map<IdAndVersion, scoped_refptr<ContentHashFetcherJob> > JobMap;
   JobMap jobs_;
 
-  // For observing the ExtensionRegistry.
-  ScopedObserver<ExtensionRegistry, ExtensionRegistryObserver> observer_;
-
   // Used for binding callbacks passed to jobs.
   base::WeakPtrFactory<ContentHashFetcher> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ContentHashFetcher);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_CONTENT_HASH_FETCHER_H_