The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2c3eb17e891e8289ec906c5de85d386b531d6989

commit 2c3eb17e891e8289ec906c5de85d386b531d6989
Author: Oystein Eftevaag <oysteine@google.com>
Date: Wed Jun 06 23:02:48 2018

Perfetto: Serialize ConvertableToTraceFormat to a JSON string field

This will act as a fallback while derived types are converted
to their own optimized proto messages.

Dependent on https://android-review.googlesource.com/c/platform/external/perfetto/+/699955
being rolled into third_party/perfetto first.

Bug:  839063 
Change-Id: I00fc5a639a770d06fbf08c60fb43d12871aa69c7
Reviewed-on: https://chromium-review.googlesource.com/1087643
Reviewed-by: Primiano Tucci <primiano@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: oysteine <oysteine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565080}
[modify] https://crrev.com/2c3eb17e891e8289ec906c5de85d386b531d6989/base/trace_event/trace_event_impl.h
[modify] https://crrev.com/2c3eb17e891e8289ec906c5de85d386b531d6989/services/tracing/perfetto/json_trace_exporter.cc
[modify] https://crrev.com/2c3eb17e891e8289ec906c5de85d386b531d6989/services/tracing/perfetto/json_trace_exporter_unittest.cc
[modify] https://crrev.com/2c3eb17e891e8289ec906c5de85d386b531d6989/services/tracing/public/cpp/perfetto/trace_event_data_source.cc
[modify] https://crrev.com/2c3eb17e891e8289ec906c5de85d386b531d6989/services/tracing/public/cpp/perfetto/trace_event_data_source_unittest.cc