Quota: Add new callback interface to WebStorageQuotaCallbacks

This is a preparation patch for introducing new Quota Management API.
The old interface will be removed after the chromium-side change[1] is landed.

[1] https://codereview.chromium.org/143923002/


BUG=332325
TEST=compile

Review URL: https://codereview.chromium.org/143913002

git-svn-id: svn://svn.chromium.org/blink/trunk@165444 bbb929c8-8fbe-4397-9dbb-9b2b20218538