Quota: Implement StorageQuotaClient

This change replaces StorageQuotaChromium with StorageQuotaClient for cleanup.


BUG=n/a
TEST=webkit/tools/layout_tests/run_webkit_tests.sh storage/\*

Review URL: https://codereview.chromium.org/133503002

git-svn-id: svn://svn.chromium.org/blink/trunk@165088 bbb929c8-8fbe-4397-9dbb-9b2b20218538