Pepper: Speed up destruction of QuotaReservation to prevent leaky tests.

Delete the QuotaReservation immediately when possible.

BUG=194304, 327759

Review URL: https://codereview.chromium.org/99333018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240201 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240201