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- Add --trace-dir=PATH to chromeos/test_runner.py
  When present, test_runner script passes the switch with
  device local path (e.g. /tmp) to gtest to generate trace
  file on device and collects the trace files back to PATH
  on host afterwards.
- Update run_gtest_benchmark.py to map the trace file path
  in the test result json collected by test_runner script
  so that processor scripts could find and computer metrics
  from the trace file.

Example usage:

For developers:
  tools/perf/run_gtest_benchmark.py
    out_${SDK_BOARD}/Release/bin/run_interactive_ui_tests
    --device=$DUT
    --gtest_filter=All/OverviewAnimationsTest.EnterExit/7
    --output-dir=/tmp/perf_output
    --output-format=histograms
    --dbus-stub --stop-ui

For perf bots:
  testing/scripts/run_performance_tests.py
    --isolated-script-test-output=/tmp/perf_output/output.json
    --non-telemetry=true
    --use-gtest-benchmark-script
    --gtest-benchmark-name=interactive_ui_tests
    tools/perf/run_gtest_benchmark.py
      out_${SDK_BOARD}/Release/bin/run_interactive_ui_tests
      --device=$DUT
      --output-format=histograms
      --dbus-stub --stop-ui

Bug: 945711
Change-Id: Ia6911921b8354d7763be96c30a8877c9d598f103
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1974587
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726402}