[tracing] Consolidate v8 reporting in memory-infra

[tracing] Consolidate v8 reporting in memory-infra

The overall plan is to make it so that all the memory-infra dumpers report,
in the "size" column, an estimation of amount of resident memory that
is causing pressure to the system.
Before this CL the v8 dumper was reporting the virtual memory size,
which is generally higher that the actual resident memory.
This CL normalizes the situation.
Also, the detailed dump about the heap objects at last GC is renamed
to reflect the information, in lack of a better solution (see
crbug.com/498779).

BUG=481504,476013

Review URL: https://codereview.chromium.org/1307173008

Cr-Commit-Position: refs/heads/master@{#347947}