[SystemInfo API] Implement storage.getAvailableCapacity API

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

 // 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.
 
 #include "chrome/browser/extensions/api/system_storage/storage_info_provider.h"
 
 #include "base/stl_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/sys_info.h"
 #include "base/threading/sequenced_worker_pool.h"
@@ skipping 69 matching lines @@
       StorageMonitor::GetInstance()->GetAllAvailableStorages();
 
   for (std::vector<StorageInfo>::const_iterator it = storage_list.begin();
        it != storage_list.end(); ++it) {
     linked_ptr<StorageUnitInfo> unit(new StorageUnitInfo());
     systeminfo::BuildStorageUnitInfo(*it, unit.get());
     info_.push_back(unit);
   }
 }
 
+double StorageInfoProvider::GetStorageFreeSpaceFromTransientIdOnFileThread(
+    const std::string& transient_id) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  std::vector<StorageInfo> storage_list =
+      StorageMonitor::GetInstance()->GetAllAvailableStorages();
+
+  std::string device_id =
+      StorageMonitor::GetInstance()->GetDeviceIdForTransientId(
+          transient_id);
+
+  // Lookup the matched storage info by |device_id|.
+  for (std::vector<StorageInfo>::const_iterator it =
+       storage_list.begin();
+       it != storage_list.end(); ++it) {
+    if (device_id == it->device_id())
+      return static_cast<double>(base::SysInfo::AmountOfFreeDiskSpace(
+                                      base::FilePath(it->location())));
+  }
+
+  return -1;
+}
+
 // static
 StorageInfoProvider* StorageInfoProvider::Get() {
   if (provider_.Get().get() == NULL)
     provider_.Get() = new StorageInfoProvider();
   return provider_.Get();
 }
 
 }  // namespace extensions