Design doc:
https://docs.google.com/document/d/1xkXj94iExFgLWc_OszTNyNGi523ARaKMWPZTeomhI4U
A lot has changed since the last patchset! I recommend revisiting this
design doc and reading the parts in green. I explain the roadmap for
what changes to expect from ETW instrumentation as well as the
instrumentation of this particular CL.

I'll do my best to answer any further questions anyone has about my
particular instrumentation or ETW in general :)

---

This is the first of a series of changelists to round out ETW
instrumentation for V8.

This changelist represents the most minimal change needed to instrument
ETW in V8. In particular, it:
  - defines and registers the ETW provider,
  - interacts minimally with the rest of V8, by hooking into the
    existing TracingController::AddTraceEvent function,
  - is designed with a platform-agnostic layer, so that event tracers
    for other platforms can be instrumented in teh future.

Some notes on instrumentation (aka I copied stuff from the design doc):

We make heavy use of the TraceLogging API to log events. It differs from
previous methods of emitting ETW events in that it doesn<E2><80><99>t
require the overhead of a separate manifest file to keep track of
metadata; rather, events using this API are self-descriptive.

Here are the five major steps to instrument the TraceLogging API:
  - Forward declare the provider (from provider-win.h)
  - Define the provider in a .cc file (from provider-win.cc)
  - Register the provider (called from v8.cc).
  - Write events (called from libplatform/tracing-controller.cc)
  - Unregister the provider (called from v8.cc)

At the base, we have an abstract provider class that encapsulates the
functionality of an event provider. These are things like registering
and unregistering the provider, and the actual event-logging.

The provider class is split into provider-win and provider-mac
(currently not instantiated) classes, with OS-dependent implementations
of the above functions.

In particular, the TraceLogging API is used only in provider-win. It is
here that we forward declare and define the provider, as well as write
ETW events.

Finally, there is a v8-provider class that serves as a top-level API and
is exposed to the rest of V8. It acts as a wrapper for the
platform-specific providers.

The .wprp file is needed so that Windows Performance Recorder knows how
to capture our events.

Some considerations:
  - Is TracingController::AddTraceEvent the best place from which to
    write my events?
  - Is src/libplatform/tracing the best place to put my instrumentation?
  - Right now, I fail the preupload because of this, which tells me my
    files are probably not in the best location:

You added one or more #includes that violate checkdeps rules.
src\init\v8.cc Illegal include: "src/libplatform/tracing/v8-provider.h"
Because of "-src/libplatform" from src's include_rules.

Change-Id: Id53e4a034c9e526524a17000da0a647a95d93edf
Bug: v8:11043
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2233407Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Sara Tang <sartang@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#71918}