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This patch adds support for interned data in typed trace points. This
helps to reduce trace size for frequently repeated data.

As an example, an interning index for base::Location could be defined as
follows:

struct InternedLocationIndex
    : public perfetto::TrackEventInternedDataIndex<
          InternedLocationIndex,
          perfetto::protos::pbzero::
              InternedData::kSourceLocationsFieldNumber,
          Location> {
  static void Add(perfetto::protos::pbzero::InternedData* interned_data,
                  size_t iid,
                  const Location& location) {
    auto* loc = interned_data->add_source_locations();
    loc->set_file_name(location.file_name());
    loc->set_function_name(location.function_name());
    loc->set_line_number(location.line_number());
  }
};

A corresponding typed trace point using the index could look like this:

  TRACE_EVENT("cat", "Name", [](perfetto::EventContext ctx) {
    auto* log = ctx.event()->set_log_message();
    size_t iid = InternedLocationIndex::Get(&ctx, FROM_HERE);
    log->set_body_iid(iid);
  }

Bug: b/156727531
Change-Id: I5a78784be688071f7373ac1655b1ce74428f7b0f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2410117
Auto-Submit: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Reviewed-by: Stephen Nusko <nuskos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#808484}