Reland again [Startup Tracing] Add --trace-config-file flag

Original CL: https://codereview.chromium.org/1315463002/
1st reland: https://codereview.chromium.org/1317333002/

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This CL adds --trace-config-file flag. Please see trace_config_file.h for details.

Design doc:
https://docs.google.com/document/d/1PgdXUOJF3WtEmYWUyGRbC2Fz2ICCZKO9jPvpLPRSHH8/edit?usp=sharing

BUG=317481, 482098
[email protected],[email protected],[email protected],[email protected],[email protected]

Review URL: https://codereview.chromium.org/1309243004

Cr-Commit-Position: refs/heads/master@{#346407}
23 files changed