PartitionAlloc: Update totalSizeOf.* counters when allocation succeeds

This CL corrects the counter values in the cases of allocation failure.

Review URL: https://codereview.chromium.org/710963002

git-svn-id: svn://svn.chromium.org/blink/trunk@185026 bbb929c8-8fbe-4397-9dbb-9b2b20218538