If a major gc happens between allocation and initialization of the
buffer, it might be already in old space. Since we need the list of
buffers to be sorted from new to old, we keep track of the last buffer
and put old buffers to the end

BUG=chromium:476032
R=hpayer@chromium.org,dslomov@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/1079923003

Cr-Commit-Position: refs/heads/master@{#27811}