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This is a small cleanup of the TraceEvent class performed
which is part of a larget bug allowing cleaning up and
reducing the generated machine code for TRACE_EVENTXXX()
macro calls (see related bug).

A first CL to perform this refactor was submitted as [1], but
later reverted because it made some tests fail mysteriously
(see http://crbug.com/899813). So the original CL was split into
several independent ones.

A first CL was submitted as [2], which actually fixed some
potential dangling pointer issues that were created from the
Initialize() and MoveFrom() methods.

This second CL removes this methods by making TraceEvent a
proper C++11 movable type, which should prevent (or at least
make it more difficult) introducing invalid states for its
instances. The goal is to see if this introduces new unexpected
test failures (which would indicate that there are still invalid
instance states used in the code base).

The third CL is [3] and re-introduces the TraceArguments helper
class on top of this one.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1318919
[2] https://chromium-review.googlesource.com/c/chromium/src/+/1340308
[3] https://chromium-review.googlesource.com/c/chromium/src/+/1318919

BUG=898794
R=primiano@chromium.org,oysteine@chromium.org,alexilin@chromium.org,chiniforooshan@chromium.org

Change-Id: I2b36885e2485d23cca199c48b2bd07d5745b00c5
Reviewed-on: https://chromium-review.googlesource.com/c/1346305
Commit-Queue: David Turner <digit@chromium.org>
Reviewed-by: Ehsan Chiniforooshan <chiniforooshan@chromium.org>
Reviewed-by: Alexandr Ilin <alexilin@chromium.org>
Reviewed-by: oysteine <oysteine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611185}