Adds a counter for large array buffers. Used to give an indication of
how common large array buffers are allocated in V8.

For the moment, we assume a 1Mb cutoff for the notion of large array
buffers.  We also use log2(length) to cleanly bucket sizes into a
histogram.

BUG=chromium:704922
R=bbudge@chromium.org,bradnelson@chromium.org,mtrofin@chromium.org

Review-Url: https://codereview.chromium.org/2792623002
Cr-Commit-Position: refs/heads/master@{#44317}