[SystemInfo API] Implement storage.getAvailableCapacity API

chrome/browser/extensions/api/system_storage/storage_info_provider.h

 // Copyright 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_BROWSER_EXTENSIONS_API_SYSTEM_STORAGE_STORAGE_INFO_PROVIDER_H_
 #define CHROME_BROWSER_EXTENSIONS_API_SYSTEM_STORAGE_STORAGE_INFO_PROVIDER_H_
 
 #include <set>
 
 #include "base/lazy_instance.h"
@@ skipping 17 matching lines @@
                           api::system_storage::StorageUnitInfo* unit);
 
 }  // namespace systeminfo
 
 typedef std::vector<linked_ptr<
     api::system_storage::StorageUnitInfo> >
         StorageUnitInfoList;
 
 class StorageInfoProvider : public SystemInfoProvider {
  public:
+  typedef base::Callback<void(const std::string&, double)>
+      GetStorageFreeSpaceCallback;
+
   // Get the single shared instance of StorageInfoProvider.
   static StorageInfoProvider* Get();
 
   // SystemInfoProvider implementations
   virtual void PrepareQueryOnUIThread() OVERRIDE;
   virtual void InitializeProvider(const base::Closure& do_query_info_callback)
       OVERRIDE;
 
+  virtual double GetStorageFreeSpaceFromTransientIdOnFileThread(
+      const std::string& transient_id);
+
   const StorageUnitInfoList& storage_unit_info_list() const;
 
   static void InitializeForTesting(scoped_refptr<StorageInfoProvider> provider);
 
  protected:
   StorageInfoProvider();
 
   virtual ~StorageInfoProvider();
 
   // Put all available storages' information into |info_|.
@@ skipping 15 matching lines @@
   virtual bool QueryInfo() OVERRIDE;
 
   static base::LazyInstance<scoped_refptr<StorageInfoProvider> > provider_;
 
   DISALLOW_COPY_AND_ASSIGN(StorageInfoProvider);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_SYSTEM_STORAGE_STORAGE_INFO_PROVIDER_H_