[SystemInfo API] Implement storage.getAvailableCapacity API

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

Index: chrome/browser/extensions/api/system_storage/storage_info_provider.cc
diff --git a/chrome/browser/extensions/api/system_storage/storage_info_provider.cc b/chrome/browser/extensions/api/system_storage/storage_info_provider.cc
index fd4208b7ad67a80788b4c73172120b283a5e70b0..b7c450358f6b3f328f93ab3ddf43ba6112f9b7df 100644
--- a/chrome/browser/extensions/api/system_storage/storage_info_provider.cc
+++ b/chrome/browser/extensions/api/system_storage/storage_info_provider.cc
@@ -88,6 +88,28 @@ void StorageInfoProvider::GetAllStoragesIntoInfoList() {
   }
 }
 
+double StorageInfoProvider::GetStorageFreeSpaceFromTransientIdOnFileThread(
+    const std::string& transient_id) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  std::vector<chrome::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<chrome::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)