bytes_processed should be used instead of bytes_to_process when
updating bytes_allocated_. Also updated the type of bytes_processed
since min() takes in 2 variables of the same type.
The code was added as part of:
https://codereview.chromium.org/2359903002

R=hpayer@chromium.org,ulan@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2380853002
Cr-Commit-Position: refs/heads/master@{#39857}