I took a look to this with Ross today. There was a surprise factor that I completely forgot about: the THreadHeapUsageTracker seems to be always on for everything (% official builds).
By looking at the v8 traces Ross was analyzing, the cost of free() calls was 1-2 order of magnitude higher.
IIRC the historical reason is that somebody (Bruce?) had concerns about perf intrusiveness on this, which seems to be confirmed by Ross' findings.

Proposed solution: can we make this:

- a cmdline argument
OR
- a chrome://flags 
OR
- something that can be dynamically turned on (one off) via devtoools, so you can make an extension button for it?

For the first two options, I'm happy to share/recycle the existing --enable-heap-profiling and have --enable-heap-profiling=task-profiler or similar (which enables only your feature, not the full heap profiler)
WDYT?

Sorry guys to trip you up like this. I like the cmdline argument.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/014a8015a054e4f8b21f7b1a163297bd9f12c22a

commit 014a8015a054e4f8b21f7b1a163297bd9f12c22a
Author: siggi <siggi@chromium.org>
Date: Thu Feb 16 16:23:54 2017

Only enable heap tracking under --enable-heap-profiling=task-profiler.

BUG= 692045 

Review-Url: https://codereview.chromium.org/2695013005
Cr-Commit-Position: refs/heads/master@{#450984}

[modify] https://crrev.com/014a8015a054e4f8b21f7b1a163297bd9f12c22a/base/base_switches.cc
[modify] https://crrev.com/014a8015a054e4f8b21f7b1a163297bd9f12c22a/base/base_switches.h
[modify] https://crrev.com/014a8015a054e4f8b21f7b1a163297bd9f12c22a/base/trace_event/memory_dump_manager.cc
[modify] https://crrev.com/014a8015a054e4f8b21f7b1a163297bd9f12c22a/base/tracked_objects.cc

Awesome, thanks for the quick fix Siggi!