Extension Storage API: expose storage quota information to extensions, via:

chrome/browser/extensions/settings/settings_api.cc

Index: chrome/browser/extensions/settings/settings_api.cc
diff --git a/chrome/browser/extensions/settings/settings_api.cc b/chrome/browser/extensions/settings/settings_api.cc
index ba277ffa7d6401563611fcd251b992f09eafabf7..f4cc62ee01a12ea10a939e61d666989a87d9a307 100644
--- a/chrome/browser/extensions/settings/settings_api.cc
+++ b/chrome/browser/extensions/settings/settings_api.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
@@ -233,4 +233,10 @@ void ClearSettingsFunction::GetQuotaLimitHeuristics(
   GetModificationQuotaLimitHeuristics(heuristics);
 }
 
+bool GetBytesInUseSettingsFunction::RunWithStorage(SettingsStorage* storage) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  result_.reset(Value::CreateIntegerValue(storage->GetBytesInUse()));
+  return true;
+}
+
 }  // namespace extensions