First step:
Enable heap profiler in runtime.
[2] https://chromium-review.googlesource.com/623813

In order to utilise heap profiler in Telemetry test (Telemetry doesn't support derivative metrics and shares the state between pageset runs) we need a switch to enable it in runtime. It can be achieved by adding DevTools handler and Mojo dispatcher (within existing memory instrumentation service). Draft CL with DevTools handler (contains some unnecessary code, not intended for landing before [2]).

Forgot the link to DevTools handler CL
[3] https://chromium-review.googlesource.com/613141

+erikchen, +ajwong and +etienneb: I don't know what are the plans on the heap profiler, but maybe they might be interested in a similar API for other purposes (heap profiler from the field and/or controlling HP via an extension).
If this is not the case (they don't need anything like this), stop reading here.
If this is the case, let's make sure that this API fits our use cases.
From my side, the comments I have right now with my visibility of things are:
- Naming wise, as the memory instrumentation stuff gets more decoupled with tracing I'd probably put this API under the Memory namespace (i.e. next to Memory.setPressureNotificationsSuppressed) and not Tracing.
- Functionality wise let's just factor in the fact that in the near future we might want to selectively enable it: 
  - Only in one mode (pseudo stack, native stack, no-stack-only-tasks)
  - Only for a given process.

What else?

Awesome, glad to see someone working on this problem!

Note that out-of-process heap-profiling is O(weeks) away from being functional, at which point we will begin discussions to deprecate/turn down the existing heap profiler. That being said, the interface/behavior are quite comparable, so all the work should carry over. The only open question is whether you want to start working directly with the OOP HP, or whether you want to continue to work with HP for now.

we had an offline chat in LON.
Given that this has already slipped off the dealine and the fact that turning the heap profiler midway through seems to introduce extra complexity, the new plan is to simplify this in the following way:
have independent stories (think to ref builds) that test the same user story with and without the heap profiler (from the beginning, using cmdline). That will remove the need of introducing a devtools api and simplify the metric.
Downside: this will make the "with-heap-profiler" time-serie susceptible to any sort of change into chrome, so the way we'd be make a use of this data is:
1) Having only a very high threshold on regressions
2) using the dual-timeline overlay (again, think to ref builds, e.g. [1]) for a-posteriori human inspection.

This will still get the ability to bisect after the fact.


[1] https://chromeperf.appspot.com/report?sid=9fba0571188acb7b4a494a8c3d8c32812561a576cf9ba5d6a370c9ce807b5446&start_rev=486073&end_rev=497440

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c554a7cf816824b363cb9ee8d1b6f2476495632b

commit c554a7cf816824b363cb9ee8d1b6f2476495632b
Author: Greg Kraynov <kraynov@chromium.org>
Date: Fri Sep 01 21:27:20 2017

[memory-infra] MDM's EnableHeapProfiling returns result.

EnableHeapProfiling now returns a result and MemoryDumpManager
now exposes GetHeapProfilingMode. Some refactofing also made.
This change is the result of splitting that CL:
https://chromium-review.googlesource.com/623813

Bug:  757747 
Change-Id: I9d0b01b65c64373ea8af48b4485865161b63ac5f
Reviewed-on: https://chromium-review.googlesource.com/643389
Commit-Queue: Grigoriy Kraynov <kraynov@chromium.org>
Reviewed-by: Siddhartha S <ssid@chromium.org>
Cr-Commit-Position: refs/heads/master@{#499305}
[modify] https://crrev.com/c554a7cf816824b363cb9ee8d1b6f2476495632b/base/trace_event/memory_dump_manager.cc
[modify] https://crrev.com/c554a7cf816824b363cb9ee8d1b6f2476495632b/base/trace_event/memory_dump_manager.h
[modify] https://crrev.com/c554a7cf816824b363cb9ee8d1b6f2476495632b/base/trace_event/memory_dump_manager_unittest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1e94989bc10b79261d67ccfeaf0e7e6308733747

commit 1e94989bc10b79261d67ccfeaf0e7e6308733747
Author: Siddhartha <ssid@chromium.org>
Date: Wed Sep 06 23:52:15 2017

Memory-infra: Heap profiler can be enabled when tracing

This is needed because new process starting when tracing and heap
profiler are enabled can get heap profiling notification later than
tracing enabled notification.
The heap profiler state should be setup when both tracing and heap
profiler are enabled. Do not call EnableHeapprofilingIfNeeded() from
constructor since the pseudo stack profiling needs to enable filtering
on TraceLog and MDM could be constructed by TraceLog in case of startup
tracing. This does not miss allocations since the heap profiling is
enabled by EnableStartupTracingIfNeeded very early (ContentMainRunner on
desktop and library loader on Android).

BUG= 757747 , 700245, 625170

Change-Id: I6fc593838dc1fa1c8450addefec782dd37ae9e5f
Reviewed-on: https://chromium-review.googlesource.com/651908
Commit-Queue: Siddhartha S <ssid@chromium.org>
Reviewed-by: Primiano Tucci <primiano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#500138}
[modify] https://crrev.com/1e94989bc10b79261d67ccfeaf0e7e6308733747/base/trace_event/heap_profiler_serialization_state.h
[modify] https://crrev.com/1e94989bc10b79261d67ccfeaf0e7e6308733747/base/trace_event/memory_dump_manager.cc
[modify] https://crrev.com/1e94989bc10b79261d67ccfeaf0e7e6308733747/base/trace_event/memory_dump_manager.h
[modify] https://crrev.com/1e94989bc10b79261d67ccfeaf0e7e6308733747/base/trace_event/memory_dump_manager_unittest.cc
[modify] https://crrev.com/1e94989bc10b79261d67ccfeaf0e7e6308733747/base/trace_event/process_memory_dump.cc

 Issue 725174  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3da60b74a4a5019c4eb4486ced60d671f0ace19a

commit 3da60b74a4a5019c4eb4486ced60d671f0ace19a
Author: Greg Kraynov <kraynov@chromium.org>
Date: Mon Oct 09 21:45:25 2017

[memory-infra] Enable heap profiling in runtime.

Introduce EnableHeapProfiling method in ClientProcess
interface of memory instrumentation service and type traits.

Bug:  757747 

Change-Id: I51c9b333996e9fcb9e7715769cc73c8349a7c3f9
Reviewed-on: https://chromium-review.googlesource.com/623813
Commit-Queue: Grigoriy Kraynov <kraynov@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Hector Dearman <hjd@chromium.org>
Reviewed-by: Siddhartha S <ssid@chromium.org>
Cr-Commit-Position: refs/heads/master@{#507499}
[modify] https://crrev.com/3da60b74a4a5019c4eb4486ced60d671f0ace19a/services/resource_coordinator/memory_instrumentation/coordinator_impl_unittest.cc
[modify] https://crrev.com/3da60b74a4a5019c4eb4486ced60d671f0ace19a/services/resource_coordinator/public/cpp/memory_instrumentation/client_process_impl.cc
[modify] https://crrev.com/3da60b74a4a5019c4eb4486ced60d671f0ace19a/services/resource_coordinator/public/cpp/memory_instrumentation/client_process_impl.h
[modify] https://crrev.com/3da60b74a4a5019c4eb4486ced60d671f0ace19a/services/resource_coordinator/public/cpp/memory_instrumentation/memory_instrumentation.typemap
[modify] https://crrev.com/3da60b74a4a5019c4eb4486ced60d671f0ace19a/services/resource_coordinator/public/cpp/memory_instrumentation/memory_instrumentation_struct_traits.cc
[modify] https://crrev.com/3da60b74a4a5019c4eb4486ced60d671f0ace19a/services/resource_coordinator/public/cpp/memory_instrumentation/memory_instrumentation_struct_traits.h
[modify] https://crrev.com/3da60b74a4a5019c4eb4486ced60d671f0ace19a/services/resource_coordinator/public/interfaces/memory_instrumentation/memory_instrumentation.mojom