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We add the following log messages:
* Error message when one of tracingCategories & traceEventsToMeasure is specified
but not the other.
* Hint users to use tools/perf/run_benchmark to get tracing based metrics

BUG=701059

Review-Url: https://codereview.chromium.org/2856463003
Cr-Commit-Position: refs/heads/master@{#468332}