Quota: Add proxy for QuotaManager::GetUsageAndQuota

This introduces proxy implementation for QuotaManager::GetUsageAndQuota in
QuotaManagerProxy.

The proxy will be used from QuotaBackend living on the File thread so that
the backend can make sure of available quota space before reserving quota.


BUG=303443
TEST=n/a
NOTRY=true

Review URL: https://codereview.chromium.org/59753008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233254 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233254