Add columns for count and size of live objects to "Allcations" view

Added "Live Count" and "Live Size" columns to the "Allocations" view. This allows to compare total amount of objects allocated by given function with the number of objects that are still live.

BUG=277984
R=alph@chromium.org

Review URL: https://codereview.chromium.org/180533010

git-svn-id: svn://svn.chromium.org/blink/trunk@168982 bbb929c8-8fbe-4397-9dbb-9b2b20218538